## Kundu And Bubble Wrap

Kundu has a Bubble Wrap and like all of us she likes popping it. The Bubble wrap has dimensions *NxM*, i.e. it has *N* rows and each row has *M* cells which has a bubble. Initially all bubbles in filled with air and can be popped.

What Kundu does is randomly picks one cell and tries to pop it, there might be a case that the bubble Kundu selected is already popped. In that case he has to ignore this. Both of these steps take 1 second of time. Tell the total expected number of seconds in which Kundu would be able to pop them all.

**Input:**

Input contains a single line containing two space seperated integers, *N M*, representing the dimension of Bubble wrap.

**Output:**

Output the required answer in one line. The answer will be considered correct, if its absolute error doesn't exceed 10^{-2}.

**Constraints:**

1 ≤ *N, M* ≤ 1000

**Sample Input #00**

```
1 1
```

**Sample Output #00**

```
1
```

**Sample Input #01**

```
1 2
```

**Sample Output #01**

```
3
```

**Sample Input #02**

```
2 2
```

**Sample Output #02**

```
8.3333333333
```

**Explanation**

*Test Case #00:* There is only one bubble, so he needs only one chance to pop it.

*Test Case #01:* Expected number of steps of popping two bubbles is 3.

*Test Case #02:* There are 4 bubbles with equal probability of popping out. Expected number of steps to pop all of them is 8.333333...

**Tested by:** Lalit Kundu