#include<stdio.h>
struct Number {
    int n;
};
int sumOfDigits(struct Number num) {
    int sum = 0;
    int temp = num.n;
    while(temp > 0) {
        sum += temp % 10;
        temp /= 10;
    } 
    return sum;
}
int main() {
    struct Number num;
    scanf("%d", &num.n);
    if (num.n < 0) {
        printf("Invalid input");
        return 0;
    }
    printf("%d", sumOfDigits(num));
    returen 0;
}