#include<bit/stdc++.h>
using namespace std;
char a[][1000];
int d[4]={-1,0,0,1},z[4]={0,-1,1,0};
struct data{
int in,jn,ans;
};
queue<data>q;
int has[80][800],ans1,f;
int main(){
int n,m;
memseta,' ',sizef(a));
cin>>m>>n;
for( i=1; i<=n; i++){
getchar();
fo(int j=1; j<=m; j++scanf("%c",&a[i][j]);
}
int x,y,x1,y1;
while(cin>>y>>x>>y1>>x1 && x!=0){
while(!q.empty())q.pop();
memset(has,0,sizeof(has));
ans1=0;
q.push(data{x,y,0});
has[x][y]=1;
a[x1][y1]=' ';
while(!q.empty()){
data t=q.front();
q.pop();
if(t.in==x1&&t.jn==y1){
ans1=t.ans;
break;
}
for(int i=0;i<4;i++){
int xn=t.in+d[i];
int yn=t.jn+z[i];
while( xn>=0 && xn<=n+1 && yn>=0 && yn<=m+1 && a[xn][yn]==' '){
if(has[xn][yn]==0){
q.push(data {xn,yn,t.ans+1});
has[xn][yn]=1;
}
xn=xn+d[i];
yn=yn+z[i];
}
}
a[x1][y1]='X'
cout<<ans1<<endl
}
}

#include<algorithm>
#include<iostream>
#include<string.h>
#include<iomanip>
#include<stdio.h>
#include<math.h>
#include<queue>
#include<stack>
using namespace std;
char a[1000][1000];
int d[4]={-1,0,0,1},z[4]={0,-1,1,0};
struct data{
int in,jn,ans;
};
queue<data>q;
int has[800][800],ans1,f;
int main(){
int n,m;
memset(a,' ',sizeof(a));
cin>>m>>n;
for(int i=1; i<=n; i++){
getchar();
for(int j=1; j<=m; j++)scanf("%c",&a[i][j]);
}
int x,y,x1,y1;
while(cin>>y>>x>>y1>>x1 && x!=0){
while(!q.empty())q.pop();
memset(has,0,sizeof(has));
ans1=0;
q.push(data{x,y,0});
has[x][y]=1;
a[x1][y1]=' ';
while(!q.empty()){
data t=q.front();
q.pop();
if(t.in==x1&&t.jn==y1){
ans1=t.ans;
break;
}
for(int i=0;i<4;i++){
int xn=t.in+d[i];
int yn=t.jn+z[i];
while( xn>=0 && xn<=n+1 && yn>=0 && yn<=m+1 && a[xn][yn]==' '){
if(has[xn][yn]==0){
q.push(data {xn,yn,t.ans+1});
has[xn][yn]=1;
}
xn=xn+d[i];
yn=yn+z[i];
}
}
}
a[x1][y1]='X';
cout<<ans1<<endl;
}
}

#include<bits/stdc++.h>
using namespace std;
char a[1000][1000];
int d[4]={-1,0,0,1},z[4]={0,-1,1,0};
struct data{
    int in,jn,ans;
};
queue<data>q;
int has[800][800],ans1,f;
int main(){
    int n,m;
    memset(a,' ',sizeof(a));
    cin>>m>>n;
    for(int i=1; i<=n; i++){
        getchar();
        for(int j=1; j<=m; j++)scanf("%c",&a[i][j]);
    }
    int x,y,x1,y1;
    while(cin>>y>>x>>y1>>x1 && x!=0){
        while(!q.empty())q.pop();
        memset(has,0,sizeof(has));
        ans1=0;
        q.push(data{x,y,0});
        has[x][y]=1;
        a[x1][y1]=' ';
        while(!q.empty()){
            data t=q.front();
            q.pop();
            if(t.in==x1&&t.jn==y1){
                ans1=t.ans;
                break;
            }
            for(int i=0;i<4;i++){
                int xn=t.in+d[i];
                int yn=t.jn+z[i];
                while( xn>=0 && xn<=n+1 && yn>=0 && yn<=m+1 && a[xn][yn]==' '){
                    if(has[xn][yn]==0){
                        q.push(data {xn,yn,t.ans+1});
                        has[xn][yn]=1;
                    }
                    xn=xn+d[i];
                    yn=yn+z[i];
                }
            }
        }
        a[x1][y1]='X';
        cout<<ans1<<endl;
      }
}