#include using namespace std; typedef long long ll; #define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i)) #define each(itr,c) for(__typeof(c.begin()) itr=c.begin(); itr!=c.end(); ++itr) #define all(x) (x).begin(),(x).end() #define pb push_back #define fi first #define se second long double sum(int n) { double ret=0; for(int i=1; i<=n; ++i) ret+=1.0/i/i; return ret; } const long double pi=acos(-1); const int N=100000000; int main() { double x; cin >>x; long double s=0,a=0; for(int i=1; i<=N; ++i) { s+=1.0L/i/i; a+=1.0L/(i+x)/(i+x); } for(int i=N+1; i<=N+(int)x; ++i) s+=1.0/i/i; cout.precision(50); cout<< a+(pi*pi/6-s) << endl; return 0; }