/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.08.14 21:22:02
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int keta_sum(int x) {
    int res = 0;
    while(x) {
        res += x % 10;
        x /= 10;
    }
    return res;
}
int main() {
    int n;cin >> n;
    for (int i = 1; i < 100; i++) {
        n = keta_sum(n);
    }
    cout << n << endl;
    return 0;
}