#include <stdio.h>
int sum;
int bala(int n)
{   sum=0;
    while(n>0)
    {
        sum=sum+n%10;
        n=n/10;
    }
    while(sum>9)
    {
        bala(sum);
    }
    return sum;
}
int n=0;
int main() {
    scanf("%d",&n);
    bala(n);
    printf("%d",sum);
    return 0;
}