#include <iostream>
#include <vector>
using namespace std;
int main(){
    int n;
    cin>>n;
    vector <double> dp(n+1);
    for (int i=1; i<=n; i++){
        for (int j=1; j<=6; j++){
            if ((1/12.0*((j+6)*(7-j))+1/6.0*(j-1)*dp[i-1])>dp[i]){
                dp[i]=1/12.0*((j+6)*(7-j))+1/6.0*(j-1)*dp[i-1];
            }
        }
    }
    cout<<dp[n]<<endl;
}