#include <fstream>
#include <cmath>

using namespace std;

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

long long  n, i, j, maxim, m;
pair<int, int> v[50003];
int main()
{
    fin>>n>>m;
    for(i=1;i<=n;i++){
        fin>>v[i].first>>v[i].second;
    }

    for(i=1;i<=n-1;i++){
        for(j=i+1;j<=n;j++){
            if(abs(v[i].first-v[j].first)+v[i].second+v[j].second>maxim)
                maxim=abs(v[i].first-v[j].first)+v[i].second+v[j].second;
        }
    }

    fout<<maxim;
    return 0;
}