#include <bits/stdc++.h>
#define ll long long
#define debug(...) fprintf(stderr,__VA_ARGS__)
using namespace std;

inline static int read(){
    int sum=0,neg=0,ch=getchar();
    while(!isdigit(ch)) neg|=(ch=='-'),ch=getchar();
    while(isdigit(ch)) sum=sum*10+(ch^48),ch=getchar();
    return neg?-sum:sum;
}

constexpr long double pi=3.14159265358979323846L;
ll sum(int l,int r){return (l+r)*(r-l+1ll)/2;}
signed main(){
    // freopen("a.in","r",stdin);
    // freopen("a.out","w",stdout);
    ll n=read(),m=read(),k=2*m/pi,s=sum(1,n),ans,t1=0,t2=0;
    for(int i=1;i<=n;i++) t1=(t1+((n-i)*2+1ll)*i),t2=(t2+(n-i)*i);
    ans=((m>1?s*2ll*m:0)+(2*k+1ll)*t2*2*m+(2*m-2*k-1ll)*n*s*2*m);
    return printf("%.10Lf\n",pi*sum(1,k)*t1/m*2*m+ans),0;
}