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  1. #include<iostream>
  2.  
  3. bool isPrime(int x) {
  4.     if(x <= 3) return x > 1;
  5.     if(x % 2 == 0 || x % 3 == 0) return false;
  6.     for(int i = 5; i * i <= x; i += 6) {
  7.         if(x % i == 0 || x % (i + 2) == 0) return false;
  8.     }
  9.     return true;
  10. }
  11.  
  12. int main() {
  13.     freopen("SNT.INP", "r", stdin);
  14.     freopen("SNT.OUT", "w", stdout);
  15.  
  16.     std::string S;
  17.     std::cin >> S;
  18.  
  19.     S = S + 'a';
  20.     int num = 0, res = -1;
  21.  
  22.     for(int i = 0; i < S.length(); ++i) {
  23.         if('0' <= S[i] && S[i] <= '9') {
  24.             num = num * 10 + (S[i] - '0');
  25.         }
  26.         else {
  27.             if(isPrime(num)) res = std::max(res, num);
  28.             num = 0;
  29.         }
  30.     }
  31.  
  32.     std::cout << res;
  33.  
  34.     return 0;
  35. }
  36.  
Success #stdin #stdout 0.01s 5324KB
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https://ideone.com/ZCsyOl
language:
C++ (gcc 8.3)
created:
3 days ago
visibility:
public

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