#include <bits/stdc++.h>
using namespace std;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
using Int = long long;
const char newl = '\n';


struct Precision{
  Precision(){
    cout<<fixed<<setprecision(12);
  }
}precision_beet;

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);
  using D = double;
  D p;
  cin>>p;

  D ans=0;
  const int MAX = 1e7;
  D res=1-p;
  for(int i=0;i<MAX;i++){
    ans+=i*res;
    res*=p;
  }
  cout<<ans<<endl;
  return 0;
}