struct Num { int n; };
int sum(struct Num x) {
    int s = 0, n = x.n;
    while (n > 0) s += n % 10, n/= 10;
    return s;
}

int main() {
    struct Num x;
    scanf("%d", &x.n);
    if (x.n < 0) 
        printf("Invalid input");
    else 
        printf("%d", sum(x));
    return 0;
}