#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using ll = long long;
int sum(int nn){
    int x=0;
    while(nn!=0){
        x+=nn%10;
        nn/=10;
    }
    return x;
}

int main() {
    int n;
    cin >> n;
    rep(i,100) n=sum(n);
    cout << n << endl;
}