#include<bits/stdc++.h>
using namespace std;
int main(){
    int x;
    float b=0,s=0,e=0;
    cin>>x;
    e=x*0.8;
    s=x*0.9;
    b=(x+e+s)/3;
    printf("%.1lf",b);
    }
/**************************************************************
	Problem: 1613
	User: linyuhang
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/