Poj Solution 2459

http://poj.org/problem?id=2459

//* @author: ccQ.SuperSupper
import java.io.*;
import java.util.*;

public class Main {
 static final int N = 2000+10;
 static int DP[] = new int[N];
 public static void main(String[]args) throws Exception{
    int n,F1,F2,Day,i,sum,a,b,j;
    //Scanner cin = new Scanner(new FileInputStream("input.txt"));
    Scanner cin = new Scanner(System.in);
    n = cin.nextInt();
    F1 = cin.nextInt();
    F2 = cin.nextInt();
    Day = cin.nextInt();
    for(i=0;i< N;++i) DP[i] = 0;
    for(i=0;i< n;++i){
        a = cin.nextInt();
        b = cin.nextInt();
        for(j=a;j<=b;++j)
            ++DP[j];
    }
    sum = 0;
    for(i=Day;i>=0;--i){
        sum+=DP[i];
        if(sum==F1-F2){
            System.out.println(i);
            break;
        }
    }
 }
}