import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Main {
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
			String str = br.readLine();
			String[] s = str.split(" ",0);
			int a = Integer.parseInt(s[0]);
			int b = Integer.parseInt(s[1]);
			int c = Integer.parseInt(s[2]);
			int d = Integer.parseInt(s[3]);
			int total = 0;
			if(a < c) {
				if(b < d) {
					total = b - c;
				}else {
					total = d - c;
				}
			}else {
				if(b < d) {
					total = b - a;
				}else {
					total = d - a;
				}
			}

			if(total >= 0) {
				System.out.println(total);
			}else {
				total = 0;
				System.out.println(total);
			}

//			long max  = 1000000007;
		}catch (Exception e) {
			System.exit(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