P2887 [USACO07NOV] Sunscreen G

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 ≤ minSPFi ≤ 1,000; minSPFi ≤ maxSPFi ≤ 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 SPFi (1 ≤ SPFi ≤ 1,000). Lotion bottle i can cover coveri 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: minSPFi and maxSPFi * Lines C+2..C+L+1: Line i+C+1 describes a sunscreen lotion bottle i with space-separated integers: SPFi and coveri

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

样例解释：给第一头奶牛涂第一种防晒霜，第二头奶牛涂第二种防晒霜。 --- 对于 $100\%$ 的数据，$1\le C,L\le 2500$，$1\le minSPF[i]\le maxSPF[i]\le 1000$，$1\le SPF[i]\le 1000$，$1\le cover[i]\le 2500$。