//qoj8027
#include <bits/stdc++.h>
using namespace std;

const long double pi = acos(-1);
int n, m;
typedef long long ll;
const ll P = 998244353;
ll b, x, z, w;
double y, a;

ll sm(ll p){
    return p * (p + 1) / 2 % P;
}

int main(){
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; ++ i){
        x += sm(n + i) - sm(i);
        y += (n + n - i - i + 1) * i * 1.0 / m;
        z += sm(n - i) + sm(i - 1);
        w += sm(n - i);
    }
    long double tmp = m;
    tmp *= 2;
    tmp /= pi;
    for(int i = 1, k = 0; i <= m; ++ i){
        int vl = (i == m) ? 1 : 2;
        if(tmp <= i){
            b += x * vl;
        } else {
            a += y * vl * i;
            b += z * vl;
        }
    }
    a *= m;
    b *= m;
    b += w * m * 2;
    if(m != 1){
        b = b + sm(n) * m * 2;
    }
    printf("%.9Lf\n", a * pi + b);
    return 0;
}