http://bailian.openjudge.cn/practice/3374

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To avoid unsightly burns while tanning, each of the C (1 <= C <= 2500) cows must cover her hide with sunscreen when they're at the beach. Cow i has a minimum and maximum SPF rating (1 <= minSPF_i <= 1,000; minSPF_i <= maxSPF_i <= 1,000) that will work. If the SPF rating is too low, the cow suffers sunburn; if the SPF rating is too high, the cow doesn't tan at all.

The cows have a picnic basket with L (1 <= L <= 2500) bottles of sunscreen lotion, each bottle i with an SPF rating SPF_i (1 <= SPF_i <= 1,000). Lotion bottle i can cover cover_i cows with lotion. A cow may lotion from only one bottle.

What is the maximum number of cows that can protect themselves while tanning given the available lotions?

* Line 1: Two space-separated integers: C and L

* Lines 2..C+1: Line i describes cow i's lotion requires with two integers: minSPF_i and maxSPF_i

* Lines C+2..C+L+1: Line i+C+1 describes a sunscreen lotion bottle i with space-separated integers: SPF_i and cover_i

A single line with an integer that is the maximum number of cows that can be protected while tanning

```3 2
3 10
2 5
1 5
6 2
4 1```

`2`

INPUT DETAILS:

3 cows; 2 lotions. Cows want SPF ratings of 3..10, 2..5, and 1..5. Lotions available: 6 (for two cows), 4 (for 1 cow). Cow 1 can use the SPF 6 lotion. Either cow 2 or cow 3 can use the SPF 4 lotion. Only 2 cows can be covered.

USACO Novermber 2007 Gold