countTriangles.cpp

//codeforces.com/contest/1355/problem/C

#include "bits/stdc++.h"
using namespace std;

#define pb push_back
#define fr(i, n) for(int i = 0; i < n; i++)
#define frr(i, n) for(int i = 1; i <= n; i++)

#define dbg(x) cout << #x << " = " << x << endl
#define all(x) x.begin(),x.end()
#define ms(x, i) memset(x, i, sizeof(x))

#define p(x) cout << x << "\n"
#define pv(x) fr(i, x.size()) cout << x[i] << " \n"[i==x.size()-1]

#define f first
#define s second

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)

typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;

const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f;

#define maxn 1123456
ll pre[maxn];

int main() {
    fastio;

    ll a, b, c, d;
    cin >> a >> b >> c >> d;
    for (ll i = a; i <= b; i++) {
        pre[i+b]++;
        pre[i+c+1]--;
    }
    frr(i, maxn-2) pre[i] += pre[i-1];
    frr(i, maxn-2) pre[i] += pre[i-1];
    ll ans = 0;
    for (ll i = c; i <= d; i++) 
        ans += pre[maxn-2] - pre[i];
    p(ans);
}