func_code_string: #include <bits/stdc++.h>   using namespace std;   const int INF = 1e9;   int main() {     long long int n, m, i, j, x, y, l = INF, u = 0;     cin >> n >> m;     if (m == 0)       cout << n - 1 << endl;     else {       for (i = 0; i < m; i++) {         cin >> x >> y;         if (y < x) swap(x, y);         u = max(u, x);         l = min(l, y);       }       if (l - u > 0)         cout << l - u << endl;       else         cout << 0 << endl;     }   }   