#include <cstdio>

int main() {
	long long int m;
	scanf("%lld", &m);
	long long int *h = new long long int[m];
	int i = 0;
	while ((scanf("%d", &h[i])) == '\n')i++;
	int num = m - i;
	num -= i;
	if (num < 0) {
		printf("NA\n");
	}
	else if (num == 0) {
		printf("1\n");
	}
	else {
		int fact1 = 1, fact2 = 1;
		for (int j = 1; j <= num + i; j++) {
			fact1 *= j;
		}
		for (int j = 1; j <= i; j++) {
			fact2 *= j;
		}

		printf("%d\n", fact1 / fact2);
	}

	return 0;
}