#include <iostream>
#include <math.h>

using namespace std;

int main()
{
float s = 2e9, v = 0,eps;
long long f=1, i=1;
cin >> eps;
while (fabs(s)>eps)
{
if(i>o) f*=i;
s = pow(-2,i)/f;
v += s;
i++;
}
cout << v << endl;
return 0;
}