Why do me is wrong

#include<iostream>
#include<cmath>
using namespace std;
int l1, r1, l2, r2, sum;
int main() {
	scanf("%d%d%d%d", &l1, &r1, &l2, &r2);
	int mi = min(l1, l2), ma = max(r1, r2);
	for (int i = mi; i <= ma; i++)
		if (i > l1 && i < r1) {
			int j = i + 1;
			if (j > l2 && j < r2) sum++;
		}
	cout << sum << endl;
}