#include <stdio.h> 
int n,m,s,t;
char ar[101][31];
int f(int a){
	int max=0;
	for(int i=0;i<m;i++){
		int cnt=0;
		for(int j=a;j<t-1;j++){
			if(ar[j][i]=='O') cnt++; 
			else break;
		}
		if(max<cnt) max=cnt;
	}
	return max;
}
int main(){
 
	scanf("%d %d\n",&n,&m);
 
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
			scanf("%c",&ar[i][j]);
		}
		scanf("\n");
	}
	scanf("%d %d\n",&s,&t);
 
	int cnt=-1;
	for(int i=s-1;i<t-1;){
		cnt++;
		if(f(i)==0){
			cnt=-1;
			break;
		}
		i+=f(i);
	}
 
	printf("%d", cnt);
}

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MTAgNwpYWFhYWFhYClhPWFhYWE8KWE9YWFhYTwpYT1hYWE9YCk9YWE9YT1gKWE9YT1hPWApPWFhPWE9YCk9YWFhYT1gKWFhYWFhYWApYWFhYWFhYCjIgOQ==

10 7
XXXXXXX
XOXXXXO
XOXXXXO
XOXXXOX
OXXOXOX
XOXOXOX
OXXOXOX
OXXXXOX
XXXXXXX
XXXXXXX
2 9