#include <bits/stdc++.h>
using namespace std;
#define FOR(i, n) for(int i = 0; i < (n); i++)
#define MEM(a, x) memset(a, x, sizeof(a))
#define ALL(a) a.begin(), a.end()
#define UNIQUE(a) a.erase(unique(ALL(a)), a.end())
typedef long long ll;
typedef pair<int, int> P;

int n;

int main(int argc, char const *argv[]) {
	ios_base::sync_with_stdio(false);
	cin >> n;
	printf("%.10lf\n", n*(n-1)*(n-2)*(n-3)*(n-4)*(n-5)/(double)(pow(6,6)));
	return 0;
}