The answer is just the maximum of sum of digits of A and sum of digits of B.

Sample Code (C++)

#include<iostream>
using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);

    int A,B;
    cin >> A >> B;
    int sumA = 0, sumB = 0;
    while(A)
    {
        sumA += A%10;
        A /= 10;
    }
    while(B)
    {
        sumB += B%10;
        B /= 10;
    }
    cout << max(sumA,sumB) << "\n";
    return 0;
}

Sample Code (Python)

def Sum(n):  
    sum = 0
    for digit in str(n):   
      sum += int(digit)        
    return sum
    
A, B = map(int,input().split())

print(max(Sum(A),Sum(B)))