#include <stdio.h>

int main(void){
    int n, k;
    double ans = 0.0;
    scanf("%d%d", &n, &k);
    int cnt1 = n*k+k, cnt2 = k;
    double deno = 1.0/cnt1;
    while(cnt1!=0){
        while(cnt2!=0){
            ans += n*deno;
            cnt2--;
        }
        cnt2 = k;
        n--;
        cnt1 -= cnt2;
    }
    printf("%f\n", ans);
    return 0;
}