ModAdd

#include <stdio.h>
#include <iostream>
#include <memory.h>
#include <string>
#include <algorithm>
#include <vector>
using namespace std;

#define sqr(a) ((a) * (a))
#define pi 3.1415926535897932384626433832795

#define TASK "a"
//#define CONTEST "1"

string s1, s2;

void Load()
{
	cin >> s1 >> s2;
	reverse(s1.begin(), s1.end());
	reverse(s2.begin(), s2.end());
}

void Solve()
{
	int n1 = s1.length();
	int n2 = s2.length();
	int n = max(n1, n2);
	string s="";

	for(int i = 0; i < n; i++)
	{
		if(i < n1 && i < n2)
			s += to_string((int)(s1[i] - '0' + s2[i] - '0')%10);
		else if(i<n1)
			s += s1[i];
		else
			s += s2[i];
	}
	reverse(s.begin(), s.end());

	cout << stoi(s);
}

int main()
{
#ifdef CONTEST
	freopen(TASK".in", "r", stdin);
	freopen(TASK".out", "w", stdout);
#endif
	
	Load();
	Solve();

	return 0;
}

Test 1

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 2

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 3

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 4

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 5

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 6

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 7

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 8

Verdict: ACCEPTED

Test 9

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

Test 10

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi