#include using namespace std; //conversion //------------------------------------------ inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;} template inline string toString(T x) {ostringstream sout;sout< inline T sqr(T x) {return x*x;} //typedef //------------------------------------------ typedef long long LL; typedef pair PII; typedef pair PLL; typedef map MII; typedef queue QI; typedef queue QPII; typedef stack SI; typedef stack SPII; typedef deque DI; typedef vector VI; typedef vector VVI; typedef vector VLL; typedef vector VVLL; typedef vector VB; typedef vector VVB; typedef vector VD; typedef vector VVD; typedef vector VS; typedef vector VVS; typedef vector VC; typedef vector VVC; typedef vector VPII; typedef vector VPLL; typedef priority_queue PQGI; //大きい順 typedef priority_queue> PQLI; typedef priority_queue PQGP; typedef priority_queue> PQLP; //container util //------------------------------------------ #define ALL(a) (a).begin(),(a).end() #define RALL(a) (a).rbegin(),(a).rend() #define PB push_back #define PF push_front #define POB pop_back #define POF pop_front #define MP make_pair #define SZ(a) int((a).size()) #define SQ(a) ((a)*(a)) #define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i) #define EXIST(s,e) ((s).find(e)!=(s).end()) #define SORT(c) sort((c).begin(),(c).end()) #define SORTR(c) sort((c).rbegin(), (c).rend()) #define LB lower_bound #define UB upper_bound #define NEXP next_permutation #define FI first #define SE second //repetition //------------------------------------------ #define FOR(i,a,b) for(int i=(a);i<(b);++i) #define REP(i,n) FOR(i,0,n) #define FORR(i,a,b) for(int i = (b-1);i>=a;i--) #define REPR(i,n) FORR(i,0,n) #define BFOR(bit,a,b) for(int bit = (a); bit < (1<<(b)); ++bit) #define BREP(bit,n) BFOR(bit,0,n) //constant //-------------------------------------------- const double EPS = 1e-10; const double PI = acos(-1.0); const int INF = INT_MAX/2; const LL LINF = LLONG_MAX/3; const int RINF = INT_MIN/2; const LL RLINF = LLONG_MIN/3; const LL MOD = 1e9+7; const LL MODD = 998244353; const int MAX = 510000; inline bool Eq(double a, double b) { return fabs(b - a) < EPS; } //other //------------------------------------------- templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b0){ if(N&1) res = res * A % M; A = A * A % M; N >>= 1; } return res; } LL fac[MAX], finv[MAX], inv[MAX]; void ConInit(LL M) { fac[0] = fac[1] = 1; finv[0] = finv[1] = 1; inv[1] = 1; for (int i = 2; i < MAX; i++){ fac[i] = fac[i - 1] * i % M; inv[i] = M - inv[M%i] * (M / i) % M; finv[i] = finv[i - 1] * inv[i] % M; } } LL COM(int n, int k, LL M){ if (n < k) return 0; if (n < 0 || k < 0) return 0; return fac[n] * (finv[k] * finv[n - k] % M) % M; } template void VCout(vector &v){ int N = SZ(v); REP(i,N){ cout << v.at(i); if(i == N-1) cout << endl; else cout << " "; } return; } int main() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(12); int a,b,c,d; cin >> a >> b >> c >> d; int ans = 0; FOR(i,a,b+1)FOR(j,c,d+1){ if(i!=j)ans++; } COUT(ans); return 0; }