#include <iostream>
using namespace std;
int n;
int h(int a){
    int b=0;
    while(a!=0){
        b=b+a%10;
        a/=10;
    }
    return b;
}
void f(int x){
    if(x<10){
        cout<<x;
    }else{
        f(h(x));
    }
}
int main(){
    cin>>n;
    f(n);
}
/**************************************************************
	Problem: 1514
	User: linzihang
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/