ModAdd

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int n, m;
string a, b;

vector<int> res;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cin >> a >> b;
	n = a.length();
	m = b.length();
	if (m > n) {
		swap(a, b);
		swap(n, m);
	}
	for (int i = 0; i < n-m; ++i) {
		res.push_back(a[i]-'0');
	}
	for (int i = n-m; i < n; ++i) {
		int eka = a[i]-'0';
		int toka = b[i-(n-m)]-'0';
		int cres = eka+toka;
		cres %= 10;
		res.push_back(cres);
	}
	bool seen = false;
	for (int c : res) {
		if (c != 0) {
			seen = true;
			cout << c;
		}
		else {
			if (seen) {
				cout << c;
			}
		}
	}
	if (!seen) {
		cout << "0";
	}
	cout << "\n";
	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