#include #include #include #include #include #include #include #include #include #include #include #include #include #include #define rep(i, a, b) for (int i = (a); i < (b); ++i) #define all(x) (x).begin(), (x).end() #define MOD 1000000007 #define int long long using ll = long long; using namespace std; const int INF = 1LL << 50; using P = pair; template bool chmin(T &a, T b) { if (a > b) { a = b; return true; } else { return false; } } template bool chmax(T &a, T b) { if (a < b) { a = b; return true; } else { return false; } } struct Setup { Setup() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); } } SETUP; signed main() { int a, b, c, d; cin >> a >> b >> c >> d; int ans = 0; rep(i, a, b + 1) rep(j, c, d + 1) { if (i != j) ans++; } cout << ans << endl; }