#include <bits/stdc++.h>   using namespace std;   int main() {     int n, s;     cin >> n >> s;     int *sa = new int[s + 1];     for (int i = 0; i < s + 1; i++) {       sa[i] = 0;     }     for (int i = 0; i < n; i++) {       int tm, tp;       cin >> tm >> tp;       if (sa[tm] < tp) {         sa[tm] = tp;       }     }     int t = 0;     for (int i = s; i > 0; i--) {       if (t < sa[i]) t = sa[i];       t++;     }     cout << t << endl;     getchar();     getchar();     return 0;   }   