ModAdd

#include <iostream>
#include <cstdio>


int main()
{
    using namespace std;
    ios::sync_with_stdio(false);

    string x, y, s="";
    cin >> x >> y;

    int xl = x.length();
    int yl = y.length();
    int l = max(xl, yl);

    int xi = 0;
    int yi = 0;

    while (l--) {
        int xx = 0;
        int yy = 0;
        if (xl-xi > yl-yi) {
            xx = x[xi++] - '0';
        }
        else if (xl-xi < yl-yi) {
            yy = y[yi++] - '0';
        }
        else {
            xx = x[xi++] - '0';
            yy = y[yi++] - '0';
        }
        s += to_string((xx+yy)%10);
    }
    size_t first = s.find_first_of('0');
    size_t last = s.find_first_not_of('0');
    if (first != string::npos)
        s.erase(first, last);
    cout << (s != "" ? s : "0");
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED