#include<iostream>
#include<cassert>
#define rep(i,n) for(i=0;i<(int)(n);i++)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

int n;

int main(){
    scanf("%d",&n);
    printf("%.8f\n",(10000.0-n)/(98*n+10000.0)*100);
    return 0;
}