#include<cstring>
#include<iostream>
#include<cstdio>

using namespace std;
int B,n,m;
bool  a[105][105],b[105][105];

bool dfs(int x,int y){
	int i,j;
	
	if (x==n+2-B){
		for (i=x;i<=n;i++)
		 for (j=1;j<=m;j++)
		  if (a[i][j]!=b[i][j]) return 0;
		return 1;
	}
	if (y==m+2-B){
		for (i=y;i<=m;i++){
			if (a[x][i]!=b[x][i]) return 0;
		}
		return dfs(x+1,1);
	}
	if (b[x][y]!=a[x][y]){
		for (i=0;i<B;i++)
		 for (j=0;j<B;j++){
		 	b[x+i][y+j]=a[x][y];
		 }
	}
	return dfs(x,y+1);
}

int main(){
	freopen("skicourse.in","r",stdin);
	freopen("skicourse.out","w",stdout);
	int i,j;
	char ch;
	scanf("%d%d",&n,&m);
	for (i=1;i<=n;i++){
		getchar();
		for (j=1;j<=m;j++){
			ch=getchar();
			if (ch=='R') a[i][j]=1;
			else a[i][j]=0;
		}
	}
	
	for (B=min(n,m);B;B--){
		memset(b,0,sizeof(b));
		if (dfs(1,1)) {
			cout<< B <<endl;
			return 0;	
		}
	}
}