#include<bits/stdc++.h>
using namespace std;
int main(){
	int x;
	float p=0,y=0,z=0;
	cin>>x;
	y=x*0.8;
	z=x*0.9;
	p=(x+y+z)/3.0;
	printf("%.1f",p);
}
/**************************************************************
	Problem: 1613
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/