找规律，自已看

#include <iostream>
/*
            1
         1  1  1
      1  2  3  2  1
   1  3  6  7  6  3  1
                            1
                         1  1
                      1  0  1  2
                   1  1  0  1  3
                1  0  0  0  1  2
             1  1  1  0  1  1  4
          1  0  1  0  0  0  1  2
       1  1  0  1  1  0  1  1  3
    1  0  0  0  0  0  0  0  1  2
 1  1  1  0
*/
int f(const int n){
    if(n <= 2){return -1;}
    int m = (n - 2) % 4;
    switch(m){
        case 1:
        case 3:
            return 2;
        case 2:
            return 3;
        case 0:
            return 4;
        default:
            break;
    }
    return -1;
}
int main(){
    int n;
    while(std::cin >> n){
        std::cout << f(n) << std::endl;
    }
    return 0;
}