#include "bits/stdc++.h";

using namespace std;

char a[1003][1003], b[1003][1003];


int main(){
    int n,m;
    cin>>n>>m;
    for (int i = 1; i <= n;i++)
        for (int j = 1; j <=m; j++)
            cin>>a[i][j];

    for (int i = 1; i <= n;i++)
        for (int j = 1; j <=m; j++)
            cin>>b[i][j];

    int cnt_a=0, cnt_ra = 0;

    for (int i = 1; i <= n;i++)
    {
        for (int j = 1; j <= m ;j++)
        {
            if (a[i][j] != b[i][j])
                cnt_a++;
            if (a[i][j] == b[i][j]){
                cnt_ra++;
            }
        }
    }
    int mx = (n*m)/2;
    if (cnt_a > mx && cnt_ra > mx)
    {
        cout<<-1;
        return 0;
    }

    for (int i = 1; i <= n;i++)
    {
        for (int j = 1; j <= m ;j++)
        {
            if (cnt_a<cnt_ra){
                cout<<a[i][j];
            }
            else{
                if (a[i][j] =='X')
                    cout<<'.';
                else
                    cout<<'X';
            }
        }
        cout<<endl;
    }
    return 0;
}

/*

3 5
X.XX.
.X...
.XX.X
X.X.X
.X...
.X...

*/