helpa svet

#include <iostream>
#include <string>
#include <sstream>
#include <vector>

int torches[1024];
int area[1024];
int light[1024];

int N;
int K;

int main()
{

    std::cin >> N;
    std::cin >> K;

    std::string str;

    for (int i = 0; i < K; i++)
    {

        std::cin >> torches[i];
        std::cin >> light[i];

    }

    for (int i = 0; i < N; i++)
        area[i] = 0;

    for (int i = 0; i < K; i++)
    {

        int istart = torches[i] - light[i];
        int iend = torches[i] + light[i];

        if (istart > 0 && iend < N)
        {

            for (int j = istart; j <= iend; j++)
            {
                area[j] = 1;
            }

        }
        else if (istart <= 0)
        {
            for (int j = 0; j <= iend; j++)
            {
                area[j] = 1;
            }
        }
        else if (iend >= N)
        {

            for (int j = istart; j <= N - 1; j++)
            {
                area[j] = 1;
            }

        }
        else if (iend >= N && istart <= 0)
        {

            for (int j = 0; j <= N - 1; j++)
            {
                area[j] = 1;
            }

        }

    }

    int count = 0;

    for (int i = 0; i < N; i++)
        if (area[i] == 0)
            count++;

    std::cout << count;

    return 0;

}