#include <stdio.h>                                                              
                                                                                
int sum_recursive(int n)                                                        
{                                                                               
    if (n == 0) {                                                           
        return 0;                                                       
    }                                                                       
                                                                                
    return n % 10 + sum_recursive(n / 10);                                  
}                                                                               
                                                                                
                                                                                
int main(void)                                                                  
{                                                                               
    int nr;                                                                 
                                                                                
    scanf("%d", &nr);                                                       
                                                                                
    printf("%d\n", sum_recursive(nr));                                      
                                                                                
    return 0;                                                               
}