#include<bits/stdc++.h>
using namespace std;
int main(){
    float x,b,c,p;
    cin>>x;
    b=x*0.8;
    c=x*0.9;
    p=(x+b+c)/3;
    printf("%.1f",p);

}

/**************************************************************
	Problem: 1613
	User: zhengzihao3
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/