#include <iostream>
#include <cmath>
using namespace std;
int main(){
double exponent = M_E, a = sqrt(2)/exponent, sum = 0, E;
cin >> E;
for (int i = 1; (a = sqrt(i+1)/(i * exponent)) >= E; i++){
exponent *= M_E;
sum += a;
}
cout << sum;
return 0;
}
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