#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int e=1, n;
double x, t, o=0;
cin >> n >> x;
for (int j=1; j<(n+1); j++)
{
t=sin(j*x);
e*=2;
o+=t/e;
}
cout << fixed << o;
return 0;
}
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