#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n;
string a,b;
char c[10001],jz;
int main() {
	scanf("%d",&n);
	if(n<10) {
		jz='0'+n;
	} else {
		jz='a'+n-10;
	}
	cin>>a>>b;
	int i=1;
	int len1=a.size() -1,len2=b.size() -1;
	while(max(len1,len2)) {
		if(len1<0) {
			c[i]=b[len2];
			len2--;
			i++;
		}
		if(len2<0) {
			c[i]=a[len1];
			len1--;
			i++;
		} else {
			c[i]=a[len1]+b[len2];
			if(c[i]>=jz) {
				c[i+1]++;
			}
			len1--;
			len2--;
			i++;
		}
	}

	for(int j=1; j<=i; j++) {
		cout<<c[j];
	}
	return 0;
}