#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000005



int main(){
	
	double p;
	cin>>p;
	
	double ans = 0.0;
	for(int i=0;i<1000000;i++){
		ans += i * pow(p,i) * (1.0-p);
	}
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
	return 0;
}