func_code_string: #include <bits/stdc++.h>   using namespace std;   bool checkC(int n) {     for (int i = 2; i * i <= n; i++) {       if (n % i == 0) return 1;     }     return 0;   }   void per(string s, int i, int &num, string &ans) {     if (i == s.length()) {       if (num != 0 && checkC(num)) {         int x = num;         int d = 0;         while (x != 0) {           x /= 10;           d++;         }         if (d > 0) {           if (d < ans.length() || ans.length() == 0) ans = to_string(num);         }       }     } else {       int k = num;       num = num * 10 + (s[i] -  0 );       per(s, i + 1, num, ans);       num = k;       per(s, i + 1, num, ans);     }   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int test;     cin >> test;     while (test--) {       int k;       cin >> k;       string s;       cin >> s;       vector<int> c(10, 0);       int ans = -1;       for (int i = 0; i < k; i++) {         int vl = s[i] -  0 ;         if (vl == 1 || vl == 4 || vl == 6 || vl == 8 || vl == 9) {           ans = vl;           break;         }         c[vl]++;       }       if (ans != -1) {         cout <<  1 n ;         cout << ans <<   n ;       } else {         if (c[2] >= 2) {           cout <<  2 n ;           cout <<  22 n ;         } else if (c[3] >= 2) {           cout <<  2 n ;           cout <<  33 n ;         } else if (c[5] >= 2) {           cout <<  2 n ;           cout <<  55 n ;         } else if (c[7] >= 2) {           cout <<  2 n ;           cout <<  77 n ;         } else {           string pa =   ;           int num = 0;           per(s, 0, num, pa);           cout << pa.length() <<   n ;           cout << pa <<   n ;         }       }     }   }   