#include <stdio.h>
#define min(a,b) (a)<(b)?(a):(b)
int n, m, i, j, a, b, ans = 1e9;
char str[55][55];
int main() {
for (i
= 0; i
< n
; i
++) scanf("%s", str
[i
]);
for (i = 0; i < n - 7; i++) for (j = 0; j < m - 7; j++) {
int cnt = 0;
for (a = i; a < i + 8; a++) for (b = j; b < j + 8; b++) {
cnt += str[a][b] == ((a&1)^(b&1) ? 'W':'B');
}
ans = min(ans, min(cnt, 64 - cnt));
}
return 0;
}
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