#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i ++)
using namespace std;
using ll = long long;
using PL = pair<ll,ll>;
using P = pair<int,int>;
constexpr int INF = 1000000000;
constexpr long long HINF = 1000000000000000;
constexpr long long MOD = 1000000007;
constexpr double EPS = 1e-4;
constexpr double PI = 3.14159265358979;

int main() {
    double p; cin >> p;
    double ans = 0.0;
    double cumprd = 1.0;
    for (int i = 0;i < 10000;i ++) {
        ans += i*cumprd;
        cumprd *= p;
    }
    ans *= 1 - p;
    printf("%.7f\n",ans);
    return 0;
}