func_code_string: #include <bits/stdc++.h>   using namespace std;   int p[1001000];   int main() {     int a, b, k;     cin >> a >> b >> k;     for (int i = 2; i <= b + 20; i++) p[i] = 1;     for (int i = 2; i <= b + 20; i++)       if (p[i])         for (int j = i + i; j <= b + 10; j = j + i) p[j] = 0;     for (int i = 1; i < b + 10; i++) p[i] = p[i] + p[i - 1];     int lo, hi, m;     lo = 0;     hi = b - a + 2;     while (lo < hi) {       int f = 1;       m = (lo + hi) / 2;       for (int i = a - 1; i + m <= b; i++) {         if (p[i + m] - p[i] < k) {           f = 0;           break;         }       }       if (f == 1) {         hi = m;       } else         lo = m + 1;     }     if (lo > b - a + 1) {       cout <<  -1  << endl;     } else       cout << lo << endl;     return 0;   }   