#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include template inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; } template inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; } //constexpr long long MAX = 5100000; constexpr long long INF = 1LL << 60; constexpr int inf = 1000000007; constexpr long long mod = 1000000007LL; //constexpr long long mod = 998244353LL; const long double PI = acos((long double)(-1)); using namespace std; typedef unsigned long long ull; typedef long long ll; typedef long double ld; int main() { /* cin.tie(nullptr); ios::sync_with_stdio(false); */ int res = 0; int a, b, c, d; cin >> a >> b >> c >> d; for (int i = a; i <= b; i++) { for (int j = c; j <= d; j++) { res += i != j; } } cout << res << endl; return 0; }