#include <stdio.h>

int count_num(long long num){
    if(num < 10){
        return num;
    }
    int sum = 0;
    while(num > 0){
        sum += num % 10;
        num /= 10;
    }
    return count_num(sum); 
}
int main(void) {
    long long n;
    scanf("%lld", &n);
    
    int ans = count_num(n);
    printf("%d", ans);

    return 0;
}