#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  long long int x, y, mx = 0, dist;
  for (int i = 0; i < n; i++) {
    cin >> x >> y;
    dist = y - (-1) * x;
    if (dist > mx) mx = dist;
  }
  cout << mx;
}
