#include <iostream.h>
int main(void)
{
    int n;
    int i,a,b;
    //int buff[81];

    cin >> n;

    if(n>81) cout<<"?";
    else if(n>0) {
        for(i=9;i>=1;i--){
            if(n%i==0) {
                a=n/i;
                b=n/a;
                if(a>9) cout<<"?";
                else cout<<a<<b;
                break;
            }
        }
    }
    if(n==0) cout<<"10";
    return 0;
}

or anyone can tell me what the traps in this problem are?

smile:)
Are you chinese?
hehe.
?='-1'