#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() {
    int a[100] = {};
    cin >> a[0];
    rep(i,99){
        while(a[i] > 0){
            a[i+1] += a[i] % 10;
            a[i] /= 10;
        }
    }
    cout << a[99] << endl;
    return 0;
}