#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,s=1,b;
    cin>>a;
    if(a<10){
        cout<<a<<endl;
    }
    else{
        while(a!=0){
            if(a%10!=0){
                s=s*(a%10);
            }
            a=a/10;
        }
        while(s>=10){
            b=s;
            s=1;
            while(b!=0){
                if(b%10!=0){
                    s=s*(b%10);
                }
                b=b/10;
            }
        }
        cout<<s<<endl;
    }
}
/**************************************************************
	Problem: 1864
	User: yangjunwen
	Language: C++
	Result: Wrong Answer
****************************************************************/