#include <stdio.h>

int count(int x){
    int sum = 0;
while(x>0){
        
        sum += x%10;
        x/=10;
    }
    if(sum>10){
        int count2 = count(sum);
        return count2;
    }
    return sum;
}

int main() {
    int n = 0;
    scanf("%d",&n);
    int sum = 0;
    int count1 = count(n);  
    
    printf("%d",count1);
    return 0;
}