#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;

int n,m;
int a[101][101],b[101][101];
int ans;
void init(){
	int i,j;
	char ch;
	cin>>n>>m;
	for (i=1;i<=n;i++)
	for (j=1;j<=m;j++){
		cin>>ch;
		if (ch=='R') a[i][j]=1;
		else a[i][j]=0;
	}
}

bool judge(int r){
	int i,j,i2,j2;
	memset(b,0,sizeof(b));
	i=1;j=1;
	while (j<=m-r+1){
		if (b[i][j]!=a[i][j]){
			for (i2=i;i2<=i+r-1;i2++)
			for (j2=j;j2<=j+r-1;j2++)
				b[i2][j2]=a[i][j];
		}
		if (i<n-r+1) i++;
		else {
			j++;
			i=1;
		}
	}
	for (i=1;i<=n;i++)
	for (j=1;j<=m;j++)
	if (a[i][j]!=b[i][j]) return false;
	
	return true;
}
			
void solve(){
	int i;
	ans=min(n,m);
	while (ans>0){
		if (judge(ans)) {
			printf("%d\n",ans);
			return;
		}
		ans--;
	}
}
	

int main(){
freopen("skicourse.in","r",stdin);
freopen("skicourse.out","w",stdout);
	init();
	solve();
	
	return 0;
}