potato field with exactly one potato on each unit square. Unfortunately, life isn't easy for : while he was away trading on the market, some farmers who were jealous of his bountiful land came and destroyed some of his potatoes. These mysterious foes worked in a methodical manner, destroying some potatoes from every column of the farm. In the column , the jealous farmers destroyed all the potatoes from row to row , inclusive.

is a diligent farmer who owns aWhen the time came for the annual harvest, potatoes to feed his family. So he decided that he would buy a tractor of width , drive it through his field horizontally exactly once, and collect any of the remaining potatoes from consecutive rows.

found that he was too busy plotting his revenge. However, he still needs to harvest at leastso that he can harvest at least potatoes.

doesn't have a lot of money to spend on a tractor, so he would like to know the minimal#### Constraints

##### Subtask 1 [20%]

##### Subtask 2 [30%]

##### Subtask 3 [50%]

#### Input Specification

The first line of input will contain three space-separated integers, , , and .

The next lines will each contain two space-separated integers, and .

#### Output Specification

Output one integer, the minimal such that can still harvest at least potatoes. If it is impossible, output `-1`

.

#### Sample Input 1

```
5 5 6
2 5
1 3
4 5
3 3
1 2
```

#### Sample Output 1

`2`

#### Explanation for Sample Output 1

The field looks like this, where `P`

represents a potato:

```
P.PP.
..PP.
..P.P
.P.PP
.P.PP
```

With a tractor of width , can harvest the last two rows for exactly potatoes.

#### Sample Input 2

```
3 4 7
2 3
1 2
1 3
2 2
```

#### Sample Output 2

`-1`

#### Explanation for Sample Output 2

Poor

only has 4 potatoes left, and therefore cannot feed his family.
## Comments

Long is needed instead of Int

Edit: Use Long Long instead of Long is a good practice

"family"

What kind of family consumes 4 * 10 ^ 10 potatoes in a season?

Lol

Sorry about the confusion with Sample Input 2, the explanation has been corrected.

I don't understand sample input 2. Aren't there only 4 potatoes left?

In sample input 2, how are there 6 potatoes left? If 2 are removed in the first column, 2 in the second, 3 in the third and 1 in the fourth, doesnt that leave 4 potatoes?

What do we do if ? Can we have a tractor with zero width?

I think you use a tractor of zero width