C++ :

#include <bits/stdc++.h>
using namespace std;
const int N = 210;
int a[N], b[N], c[N], n;
void convert(int a[], string s)
{
	int len = s.size();
	for (int i = 0; i < len; i++)
		if (s[i] >= '0' && s[i] <= '9') 
			a[len-i-1] = s[i] - '0';
		else
			a[len-i-1] = s[i] - 'a' + 10;
}

int main()
{
	cin >> n;
	string s1, s2;
	cin >> s1 >> s2;
	int len1 = s1.size();
	int len2 = s2.size();
	convert(a, s1);
	convert(b, s2);
	int len = max(len1, len2);
	int t = 0;
	for (int i = 0; i < len; i++)	
	{
		t += a[i] + b[i];
		c[i] = t % n;
		t /= n;
	}
	if (t > 0) c[len++] = t;
	for (int i = len - 1; i >= 0; i--)
		if (c[i] >= 10) cout << char(c[i] + 'a' - 10);
		else cout << c[i];
	return 0;
}