func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 1000010;   int cnt[N];   int a, b, n;   void genPrime() {     for (int i = 2; i < N; ++i) cnt[i] = 1;     for (int i = 2; i <= 1000; ++i)       if (cnt[i])         for (int j = i * i; j < N; cnt[j] = 0, j += i)           ;     for (int i = 1; i < N; ++i) cnt[i] += cnt[i - 1];   }   bool chk(int x) {     for (int i = a; i + x - 1 <= b; ++i) {       int j = i + x - 1;       if (cnt[j] - cnt[i - 1] < n) return false;     }     return true;   }   int main() {     int i, j, k;     genPrime();     scanf( %d%d%d , &a, &b, &n);     if (cnt[b] - cnt[a - 1] < n) {       printf( -1 n );       return 0;     }     int low = 1, up = b - a + 1;     while (up > low) {       int mid = (up + low) / 2;       if (chk(mid))         up = mid;       else         low = mid + 1;     }     printf( %d n , up);     return 0;   }   