1080 행렬

#include <stdio.h>
 
int arr[51][51] = { 0 }, brr[51][51] = { 0 }, crr[51][51] = { 0 };
 
void change(int y, int x) {
    for (int i = y; i < y + 3; i++) {
        for (int j = x; j < x + 3; j++) {
            if (crr[i][j] == 0)
                crr[i][j] = 1;
            else
                crr[i][j] = 0;
        }
    }
}
 
int main() {
    int n, m;
    scanf("%d %d", &n, &m);
 
    for (int i = 0; i < n; i++) {
        char line[51];
        scanf("%s", &line);
 
        for (int j = 0; j < m; j++) {
            arr[i][j] = (int)(line[j] - '0');
        }
    }
 
    for (int i = 0; i < n; i++) {
        char line[51];
        scanf("%s", &line);
 
        for (int j = 0; j < m; j++) {
            brr[i][j] = (int)(line[j] - '0');
 
            if (arr[i][j] != brr[i][j])
                crr[i][j] = 1;
        }
    }
 
    int rst = 0;
    for (int i = 0; i + 2 < n; i++) {
        for (int j = 0; j + 2 < m; j++) {
            if (crr[i][j] == 1) {
                change(i, j);
                rst++;
            }
        }
    }
 
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (crr[i][j] == 1) {
                printf("-1");
                return 0;
            }
        }
    }
 
    printf("%d", rst);
}