import java.util.*;

public class Main{
	public static void main(String[] args){
	    Scanner scanner = new Scanner(System.in);
	    int[] array = new int[4];
	    int ans=-1;
	    for(int i=0;i<4;i++){   
		array[i]=scanner.nextInt();
	    }
	    if(array[0]<=array[2]){
		if(array[1]<=array[3])ans=array[1]-array[2];
		if(array[3]<=array[1])ans=array[3]-array[2];
	    }
	    if(array[2]<array[0]){
		if(array[1]<=array[3])ans=array[1]-array[0];
		if(array[3]<=array[1])ans=array[3]-array[0];
	    }
	    if(ans<0)ans = 0;
		System.out.println(ans);
	}
}
/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