C++ :

#include <algorithm>
#include <cstdio>
using namespace std;
int main() {
	int n, i, j, k;
	scanf("%d", &n);
	k = n / 2;
	for (i = 1; i <= n; i++) {
	for (j = 1; j <= n; j++) {
	if (abs(k - i + 1) + abs(k - j + 1) == k)
	printf("#");
	else
	printf(".");
	}
	printf("\n");
	}
	return 0;
}