/*

水题

*/

#include<iostream>

#include<cstdio>

#include<string>

#include<cstring>

#include<algorithm>

#include<vector>

using namespace std;

int l,k;

string s,num;

int main(){

    freopen("love.in","r",stdin);

    freopen("love.out","w",stdout);

    cin>>l>>k>>s>>num;

    for(int i = ;i < l;i++){

        int j = i % k;

        char tmp =  + ((s[i] - ) + (num[j] - )) % ;

        s[i] = tmp;

    }

    cout<<s;

    return ;

}