#include using namespace std; typedef signed long long ll; #undef _P #define _P(...) (void)printf(__VA_ARGS__) #define FOR(x,to) for(x=0;x<(to);x++) #define FORR(x,arr) for(auto& x:arr) #define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++) #define ALL(a) (a.begin()),(a.end()) #define ZERO(a) memset(a,0,sizeof(a)) #define MINUS(a) memset(a,0xff,sizeof(a)) //------------------------------------------------------- void solve() { int i,j,k,l,r,x,y; string s; double X; cin>>X; double ret=0; i=1200000000; X+=i; for(;i>=100;i-=3) { double a=(X*X); double b=(X-1)*(X-1); double c=(X-2)*(X-2); double ab=a*b; ret += (ab+c*(a+b))/(ab*c); X-=3; } for(;i>=1;i--) { ret += 1.0/(X*X); X--; } _P("%.12lf\n",ret); } int main(int argc,char** argv){ string s;int i; if(argc==1) ios::sync_with_stdio(false), cin.tie(0); FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin); solve(); return 0; }