#include <iostream>
using namespace std;
int main()
{
    int n, m;
    cin >> n >> m;
    int maxTime = 0;
    int x, y;
    for (int i = 0; i < m; i++)
    {
        cin >> x >> y;
        int time = (x - 1) + (y - 1);
        if (time > maxTime)
            maxTime = time;
    }
    cout << maxTime << endl;
    return 0;
}