import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.Scanner;

public class NetworkPacket {

    static class Request {
        int arrivalTime;
        int processTime;

        Request(int arrivalTime, int processTime) {
            this.arrivalTime = arrivalTime;
            this.processTime = processTime;
        }

    }

    static class Response {
        boolean dropped;
        int startTime;

        Response(boolean dropped, int startTime) {
            this.dropped = dropped;
            this.startTime = startTime;
        }
    }

    static class Buffer {
        private int capacity;
        private Deque<Integer> finishTime;

        // My addition to the starter file
        private int runningTimeCounter = 0;
        // End of my addition to the starter file

        Buffer(int capacity) {
            this.capacity = capacity;
            this.finishTime = new LinkedList<>();
        }

        Response processRequest(Request request) {
            if (runningTimeCounter < request.arrivalTime)
                if (finishTime.size() == 0)
                    runningTimeCounter = request.arrivalTime;
                else if (finishTime.getLast() < request.arrivalTime)
                    runningTimeCounter = request.arrivalTime;

            while (finishTime.size() > 0) {
                int j = finishTime.getFirst();
                if (j <= request.arrivalTime)
                    finishTime.pop();
                else
                    break;
            }

            if (finishTime.size() >= capacity) {
                return new Response(true, -1);
            }
            Response response = new Response(false, runningTimeCounter);
            runningTimeCounter = runningTimeCounter + request.processTime;
            if (finishTime.size() > 0)
                finishTime.addLast(finishTime.getLast() + request.processTime);
            else
                finishTime.addLast(runningTimeCounter);
            return response;
        }
    }

    private static ArrayList<Request> ReadQueries(Scanner scanner) {
        int requests_count = scanner.nextInt();
        ArrayList<Request> requests = new ArrayList<>();
        for (int i = 0; i < requests_count; ++i) {
            int arrival_time = scanner.nextInt();
            int process_time = scanner.nextInt();
            requests.add(new Request(arrival_time, process_time));
        }
        return requests;
    }

    static ArrayList<Response> processRequests(ArrayList<Request> requests, Buffer buf) {
        ArrayList<Response> responses = new ArrayList<>();
        for (Request request : requests) {
            responses.add(buf.processRequest(request));
        }
        return responses;
    }

    private static void PrintResponses(ArrayList<Response> responses) {
        for (Response response : responses) {
            if (response.dropped) {
                System.out.println(-1);
            } else {
                System.out.println(response.startTime);
            }
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int bufferMaxSize = scanner.nextInt();
        Buffer buffer = new Buffer(bufferMaxSize);

        ArrayList<Request> requests = ReadQueries(scanner);
        ArrayList<Response> responses = processRequests(requests, buffer);
        PrintResponses(responses);
    }
}