func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int mx = 0, i, n, m, d, h, ld, lh;     cin >> n >> m;     for (i = 0; i < m; i++) {       cin >> d >> h;       if (i == 0) {         ld = d;         lh = h;         mx = lh + ld - 1;         continue;       }       if (abs(h - lh) > d - ld) {         cout <<  IMPOSSIBLE ;         return 0;       }       if (h - lh < 0)         mx = max(mx, lh + (d - ld - abs(h - lh)) / 2);       else         mx = max(mx, h + (d - ld - abs(h - lh)) / 2);       ld = d;       lh = h;     }     mx = max(mx, lh + n - ld);     cout << mx;     return 0;   }   