我的代码：

#include <bits/stdc++.h>
  using namespace std;
int n,m,s=1000000,t,i,j,k,l;
char a[51][51];
int main()
{
	cin>>n>>m;
	for (i=1;i<=n;i++)
	{
		for (j=1;j<=m;j++)
		{
			cin>>a[i][j];
			//a[i][j]=getchar();
		}
	}
	for (i=1;i<=n-2;i++)
	{
		for (j=i+1;j<=n-1;j++)
		{
			t=0;
			for (k=1;k<=i;k++)
			{
				for (l=1;l<=m;l++)
				{
					if (a[k][l]!='W') t++;
				}
			}
			for (k=i+1;k<=j;k++)
			{
				for (l=1;l<=m;l++)
				{
					if (a[k][l]!='B') t++;
				}
			}
			for (k=j+1;k<=n;k++)
			{
				for (l=1;i<=m;l++)
				{
					if (a[k][l]!='R') t++;
				}
			}
			s=min(s,t);
		}
	}
	cout<<s<<endl;
	return 0;
}