#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;
	}

    return 0;
}
/**************************************************************
	Problem: 1846
	User: admin
	Language: C++
	Result: Accepted
	Time:67 ms
	Memory:2072 kb
****************************************************************/