#include <bits/stdc++.h>

using i64 = long long;

using F = long double;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    std::cout << std::fixed << std::setprecision(10);
    
    int n;
    F a;
    std::cin >> n >> a;
    
    F ans = 0;
    
    ans += (n - 1) * (1 - a) + (1 - n * a) / n;
    
    for (int i = 1; i <= n; i++) {
        ans -= (1 - n * a) / i;
    }
    ans /= (n - 1);
    ans = 1 - ans;
    
    std::cout << ans << "\n";
    
    return 0;
}