#include <bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
using namespace std;
typedef double db;

int n,m;
db pi=acos(-1.0);
void work()
{
    cin>>n>>m;
    m*=2;
    db res=0;
    For(i,1,n){
        For(j,i,n){
            if(j!=i)res+=1.0l*(j-i)*m*m;
            db now=0;
            For(k,0,m-1){
                db d1=min(k,m-k)*pi*2/m;
                db d2=2;
                now+=min(d1,d2);
            }
            now*=i;
            now*=m;
            if(i==j) now/=2;
            res+=now;
        }
    }
    if(m!=2){
        db sum=0;
        For(i,1,n)sum+=i;
        sum*=m;
        res+=sum;
    }
    printf("%.12lf\n",res);
}
int main()
{
    //cout<<"pi "<<pi<<"\n";
	int T=1;
	while(T--){
        work();
	}
	return 0;
}