#include <iostream>
using namespace std;
int main() {
    int m,n;
    int left=0,right=0,top=0,bottom=0;
    cin>>m>>n;
    char array[m][n];
    
    for(int i=0;i<m;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>array[i][j];
        }
    }
    right=1;
    int i=0,j=0;
    for(int tst=0;tst<m*n;tst++)
    {
        if(right==1)
        {
            if(array[i][j]=='?'||j==n-1)
            {
                if(array[i][j]!='?') 
                    cout<<array[i][j];
                right=0;
                bottom=1;
                i++;
                continue;
                
            }
            cout<<array[i][j];
            array[i][j]='?';
            j++; 
        }
        else if(left==1)
        {
            if(array[i][j]=='?'||i==0)
            {
                if(array[i][j]!='?') 
                    cout<<array[i][j];
                left=0;
                top=1;
                i--;
                continue;
            }
            cout<<array[i][j];
            array[i][j]='?';
            j--;
        }
        else if(top==1)
        {
            if(array[i][j]=='?'||j==0)
            {
                if(array[i][j]!='?') 
                    cout<<array[i][j];
                right=1;
                top=0;
                j++;
                continue;
            }
            cout<<array[i][j];
            array[i][j]='?';
            i--;
        }
        else if(bottom==1)
        {
            if(array[i][j]=='?'||i==m-1)
            {
                if(array[i][j]!='?') 
                    cout<<array[i][j];
                bottom=0;
                left=1;
                j--;
                continue;
            }
            cout<<array[i][j];
            array[i][j]='?';
            i++;
        }
    }
    return 0;
}