#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

int main(){
  double p;
  cin >> p;
  double ans = 0;
  int co = 1;
  double n = p, bf = 1;
  while(1){
    ans += (co-1)*(bf-n);
    bf = n;
    n *= p;
    if(n < 0.000000001) break;
    co++;
  }
  cout << fixed << setprecision(10) << ans << endl;
  return 0;
}