#include <iostream>
#include <vector>
using namespace std;
int main() {
    int n;
    cin>>n;
        while(n>=10){
            int sum=0;
            while (n>0){
                sum=sum+n%10;
                n/=10;
        }
            n=sum;
        }
    cout<<n<<endl;
        return 0;
}