#include using namespace std; #define int long long #define vvi vector> #define vec vector #define pq priority_queue #define all(v) (v).begin(), (v).end() #define uniqueV(x) sort(x.begin(), x.end()); x.erase(unique(x.begin(), x.end()), x.end()); #define rep(i, n) for (int (i) = (0); (i) < (n); ++(i)) #define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i)) #define dbg(x) cerr << #x << ": " << x << endl; #define dbg2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<(value) << endl; #define line() cerr << "---------------" << endl; const int dx[] = {1, -1, 0, 0}; const int dy[] = {0, 0, -1, 1}; const double PI = 3.14159265358979323846; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b void print1(T begin, T end) { while (begin != end) { cout << (*begin) << " "; *begin++; } cout << endl; } template void print2(T Array, int height, int width) { for (int i = 0; i < height; i++) { for (int j = 0; j < width; j++) { cout << " " << Array[i][j]; } cout << endl; } } void print() { std::cerr << endl; } template void print(Head&& head, Tail&&... tail) { std::cerr << head << " "; print(std::forward(tail)...); } template void Add(T &a, const T &b, const T &mod=1000000007) { int val = ((a % mod) + (b % mod)) % mod; if (val < 0) { val += mod; } a = val; } template auto vectors(X x, T a) { return vector(x, a); } template auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector(x, cont); } // ------------------------------------------------------------------------------------------ signed main() { int a, b, c, d; cin >> a >> b >> c >>d; int ans = 0; for (int i = a; i <= b; i++) { if (i >= c and i <= d) { ans += d - c; } else { ans += d - c + 1; } } cout << ans << endl; return 0; }