C++ :

#include<bits/stdc++.h>
using namespace std;

int cnt[128];
char a[3010][3010];
int n;

void change(int &x, int &y) {
	int nx = y, ny = n + 1 - x;
	x = nx;
	y = ny;
}

int main() {
	cin >> n;
	for(int i = 1; i <= n; ++i)
		for(int j = 1; j <= n; ++j)
			cin >> a[i][j];
	int ans = 0;
	for(int i = 1; i <= n; ++i) {
		for(int j = 1; j <= n; ++j) {
			int x = i, y = j;
			cnt['0'] = cnt['1'] = 0;
			cnt[a[x][y]] ++;
			change(x, y);
			cnt[a[x][y]] ++;
			change(x, y);
			cnt[a[x][y]] ++;
			change(x, y);
			cnt[a[x][y]] ++;
			ans += min(cnt['0'], cnt['1']);
		}
	}
	cout << ans / 4 << endl;
	return 0;
}