#include <bits/stdc++.h>
using namespace std;
#define int long long
typedef pair<int,int> P;
int INF = 1e9+7;
int mod = 1e9+7;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
signed main() {
    int N;
    cin >> N;
    for(int i = 0; i < 99; i++) {
        int cnt = 0;
        while(N) {
            cnt += N%10;
            N/=10;
        }
        N = cnt;
    }
    cout << N << endl;
}