#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

ifstream fin("orase.in");
ofstream fout("orase.out");

int poz[50001], lung[50001];

int main()
{
    int n, m, i, j, d, l, s, sm = 0;
    fin >> n >> m;
    for(i = 1; i <= n; ++i)
    {
        fin >> d >> l;
        poz[i] = d;
        lung[i] = l;
    }
    for(i = 1; i <= n; ++i)
    {
        for(j = i; j <= n; ++j)
        {
            s = abs(poz[i] - poz[j]) + lung[i] + lung[j];
            sm = max(s, sm);
        }
    }
    fout << sm;

    return 0;
}