#include <bits/stdc++.h>
using namespace std;
int main() {
    int x;
    cin>>x;
    float e=x*0.8;
    float s=x*0.9;
    float p=(e+s+x)/3;
	printf("%.1f",p);
    return 0;
}
/**************************************************************
	Problem: 1613
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/