#include <iostream>
using namespace std;
int main(){
    int N,a[100]={0};
    cin >> N;a[0]=N;
    for(int i=0;i+1<100;i++){
        while(a[i]>0){
            a[i+1]+=a[i]%10;a[i]/=10;
        }
    }
    cout << a[99] << endl;
    return 0;
}