func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 1e6 + 5;   bool isprime[N] = {1, 1, 0};   int sum[N] = {};   void YesIcan() {     for (int i = 2; i * i <= N; ++i) {       for (int j = i * i; j <= N; j += i) isprime[j] = true;     }   }   int main() {     YesIcan();     int a, b, k;     cin >> a >> b >> k;     for (int i = a; i <= b; ++i) {       sum[i] = sum[i - 1];       if (!isprime[i]) ++sum[i];     }     if (sum[b] < k) {       cout << -1;       return 0;     }     int i = a - 1, l = 1;     for (; i <= b - l; ++i) {       while (sum[i + l] - sum[i] < k && l <= b - a + 1 && i + l <= b) ++l;     }     cout << l;   }   