#include <fstream>
std::ifstream f("orase.in");
std::ofstream g("orase.out");
int d,l,st,dr;
int main()
{
    f>>d>>l;
    while(f>>d>>l)
        st=std::max(st,d+l),dr=std::max(dr,l-d);
    g<<st+dr;
}