1100C NN and the Optical Illusion

推公式，水题。cos（）函数是默认弧度制的

 #include <iostream>
 #include <cstring>
 #include <string>
 #include <map>
 #include <set>
 #include <algorithm>
 #include <fstream>
 #include <cstdio>
 #include <cmath>
 #include <stack>
 #include <queue>
 using namespace std;
 const double Pi=3.14159265358979323846;
 typedef long long ll;

 int main()
 {
     double n,a;
     cin>>n>>a;double s=/n*1.0/*Pi;
     double ans=(sqrt()*a)/(sqrt()-sqrt(-cos(s)))-a;
     printf("%.7lf\n",ans);
     return ;
  }