#include <iostream>
#include <queue>
#include <vector>
//#include <gtest/gtest.h>

struct Request {
	Request(int arrival_time, int process_time) :
			arrival_time(arrival_time), process_time(process_time) {
	}

	int arrival_time;
	int process_time;
};

struct Response {
	Response(bool dropped, int start_time) :
			dropped(dropped), start_time(start_time) {
	}

	bool dropped;
	int start_time;
};

class Buffer {
public:
	Buffer(int capacity) :
			capacity_(capacity), finish_time_() {
	}

	Response Process(const Request &request) {
		// write your code here
		if (runningTimeCounter_ < request.arrival_time) {
			if (finish_time_.size() == 0)
				runningTimeCounter_ = request.arrival_time;
			else if (finish_time_.back() < request.arrival_time)
				runningTimeCounter_ = request.arrival_time;
		}
		while (finish_time_.size() > 0) {
			int j = finish_time_.front();
			if (j <= request.arrival_time)
				finish_time_.pop();
			else
				break;
		}

		if (finish_time_.size() >= capacity_) {
			return Response(true, -1);
		}
		Response response = Response(false, runningTimeCounter_);
		runningTimeCounter_ = runningTimeCounter_ + request.process_time;
		if (finish_time_.size() > 0)
			finish_time_.push(finish_time_.back() + request.process_time);
		else
			finish_time_.push(runningTimeCounter_);
		return response;

	}
private:
	size_t capacity_;
	std::queue<int> finish_time_;
	int runningTimeCounter_ = 0;
};

std::vector<Request> ReadRequests() {
	std::vector<Request> requests;
	int count;
	std::cin >> count;
	for (int i = 0; i < count; ++i) {
		int arrival_time, process_time;
		std::cin >> arrival_time >> process_time;
		requests.push_back(Request(arrival_time, process_time));
	}
	return requests;
}

std::vector<Response> ProcessRequests(const std::vector<Request> &requests,
		Buffer *buffer) {
	std::vector<Response> responses;
	for (size_t i = 0; i < requests.size(); ++i)
		responses.push_back(buffer->Process(requests[i]));
	return responses;
}

void PrintResponses(const std::vector<Response> &responses) {
	for (size_t i = 0; i < responses.size(); ++i)
		std::cout << (responses[i].dropped ? -1 : responses[i].start_time)
				<< std::endl;
}

//TEST(ProcessRequests, t) {
//    int bufferMaxSize = 1;
//    Buffer buf = Buffer(bufferMaxSize);
//    std::vector<Request> requests;
//    std::vector<Response> responses = ProcessRequests(requests, &buf);
//    ASSERT_EQ(0, responses.size());
//}
//
//TEST(ProcessRequests, t1) {
//    int bufferMaxSize = 1;
//    Buffer buf = Buffer(bufferMaxSize);
//    std::vector<Request> requests = {Request(0, 1)};
//    std::vector<Response> responses = ProcessRequests(requests, &buf);
//    ASSERT_EQ(1, responses.size());
//    ASSERT_EQ(false, responses[0].dropped);
//}
//
//TEST(ProcessRequests, t2) {
//    int bufferMaxSize = 1;
//    Buffer buf = Buffer(bufferMaxSize);
//    std::vector<Request> requests = {Request(0, 1), Request(0, 1)};
//    std::vector<Response> responses = ProcessRequests(requests, &buf);
//    ASSERT_EQ(2, responses.size());
//    ASSERT_EQ(false, responses[0].dropped);
//    ASSERT_EQ(0, responses[0].start_time);
//    ASSERT_EQ(true, responses[1].dropped);
//}
//
//TEST(ProcessRequests, t3) {
//    int bufferMaxSize = 1;
//    Buffer buf = Buffer(bufferMaxSize);
//    std::vector<Request> requests = {Request(0, 1), Request(1, 1)};
//    std::vector<Response> responses = ProcessRequests(requests, &buf);
//    ASSERT_EQ(2, responses.size());
//    ASSERT_EQ(false, responses[0].dropped);
//    ASSERT_EQ(0, responses[0].start_time);
//    ASSERT_EQ(false, responses[1].dropped);
//    ASSERT_EQ(1, responses[1].start_time);
//}

int main() {
	int size;
	std::cin >> size;
	std::vector<Request> requests = ReadRequests();

	Buffer buffer(size);
	std::vector<Response> responses = ProcessRequests(requests, &buffer);

	PrintResponses(responses);
	return 0;
}