import java.util.Scanner;

class Main{
	public static void main(String arg[]) {
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		int C = sc.nextInt();
		int D = sc.nextInt();	
		sc.close();
		
		System.out.println(subAbs(A, B, C, D));
	}
	
	public static int subAbs(int A, int B, int C, int D){
		int sub = Math.min(B, D) - Math.max(A, C);
		if( sub > 0) {
			return sub;
		}else {
			return 0;
		}
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz