import std.stdio, std.array, std.conv, std.string, std.algorithm, std.math, std.regex;

void main(){
    int n, k;
    readf("%d %d\n", &n, &k);
    double rateVal, rate;
    rate = 0;
    rateVal = 1/( to!(float)((n+1)*k) );
	for(int i; i<=n; i++){
        rate += rateVal*to!(double)(i*k);
    }
    rate.writeln();
}



// 読み込み用
T readOne(T=size_t)(){
    return readln().chomp().split[0].to!T();
}

T[] readLine(T=size_t)(string op=" "){
	T[] ol;
	foreach(string elm; readln().chomp().split(op)){
		ol ~= elm.to!T();
	}
	return ol;
}