#include <iostream> #include <algorithm> using namespace std; int main(){ int a, b, c, d; cin >> a >> b >> c >> d; if(b < c || d < a){ cout << (b - a + 1) * (d - c + 1) << "\n"; return 0; } cout << (b - a + 1) * (d - c + 1) - (min(d, b) - max(a, c) + 1) << "\n"; }