CCF 买菜 java100分

package ccf第二题;

import java.util.Scanner;

public class 买菜 {
	public static void main(String[] args) {
		int[]flag = new int[1000001];
		Scanner in = new Scanner(System.in);
		int num = in.nextInt();
		for (int i = 0; i < num*2; i++) {
			int start = in.nextInt();
			int end = in.nextInt();
			for (int j = start; j <end; j++) {
				flag[j]++;
			}
		}
		int c = 0;
		for (int i : flag) {
			if(i == 2)
				c++;
		}
		in.close();
		System.out.println(c);
		
	}
}