不知什么问题，全WA，有大佬可以帮忙找下问题吗

#include <bits/stdc++.h>
#define ll long long
#define INF 0x3fffffff
using namespace std;

char c[55][55];
int a[3][55], ans, sum;

int main()
{
	int n, m, x;
	
	scanf("%d%d\n", &n, &m);
	for(int i = 1; i <= n; i++)
	{
		for(int j = 1; j <= m; j++)
		{
			c[i][j] = getchar();
			if(c[i][j] != 'W')
				a[0][i]++;
			if(c[i][j] != 'B')
				a[1][i]++;
			if(c[i][j] != 'R')
				a[2][i]++;
		}
		getchar();
	}

	ans = INF;

	for(int i = 2; i < n; i++)
		for(int j = i + 1; j <= n; j++)
		{
			sum = 0;
			for(x = 1; x < i; x++) sum += a[0][x];
			for(x = i; x < j; x++) sum += a[1][x];
			for(x = j; x <= n; x++) sum += a[2][x];
			if(sum < ans) ans = sum;
		}
	
	printf("%d", ans);
	return 0;
}

十分感谢