Submission #3208137

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Source Code Expand

#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int N; cin >> N;
	int C[100];
	rep(i, N) cin >> C[i];
	double ans = 0;
	rep(i, N) {
		int tmp = 0;
		rep(j, N) {
			if (i == j) continue;
			if (C[i] % C[j] == 0) tmp++;
		}
		if (tmp % 2 == 1) ans += 1 / 2.0;
		else ans += (tmp + 2) / (double)(tmp * 2 + 2);
	}
	cout << fixed << setprecision(12) << ans << endl;

    return 0;
}

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