#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define mod 1000000007

int main(){
    int n;cin>>n;
    int summ = 0;
    while(n>9){
        int summ = 0;
        while(n>9){
            summ = summ + n%10;
            n = n/10;
        }
        summ = summ + n;
        n = summ;
    }
    cout<<n;
    return 0;
}
