#include <bits/stdc++.h>
using namespace std;
const double pi=3.141592653589;
int n,m,b[1005][1005];
double ans,sum;
int cyc(int x,int y){
    return min(abs(y-x),2*m-y+x);
}
int main(){
    cin>>n>>m;
    double angle=pi/(double)m;
    for (int i=1;i<=2*m;i++){
        for (int j=i+1;j<=2*m;j++) {
            if ((double)cyc(i,j)*angle>2.0) {
                sum+=2.000;
            }
            else {
                sum+=(double)cyc(i,j)*angle;
            }
        }
    }
    //sum+=2.0*(double)m;
 //   cout<<fixed<<setprecision(10)<<sum<<"\n";
    for (int i=1;i<=n;i++){
        ans+=sum*(double)i;
        if (m!=1) ans+=2.0*m*i;
        for (int j=i+1;j<=n;j++){
            ans+=(j-i)*4*m*m+sum*i*2;
        }
    }
    
    cout<<fixed<<setprecision(10)<<ans<<"\n";
    
}