3 USACO

//< in.txt > out.txt

#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <queue>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <stack>
#include <utility>
#include <vector>
#include <fstream>

#define INF 1000000000
#define FOR(i, a, b) for(int i=int(a); i<int(b); i++)
#define FORC(cont, it) for(typeof((cont).begin()) it = (cont).begin(); it != (cont).end(); it++)
#define pb push_back

using namespace std;

typedef long long ll;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;

#define maxN 100000

struct Data {
    ll cost;
    bool operator <(const Data &r) const {
        return cost > r.cost;
    }
};

ll A[maxN], B[maxN];

int main() {
    ifstream in("landscape.in");
    ofstream out("landscape.out");
    ll N, X, Y, Z;
    while (in >> N >> X >> Y >> Z) {
        FOR(i, 0, N) in >> A[i] >> B[i];
        ll acum = 0, ans = 0;
        priority_queue<Data> q1, q2;
        FOR(i, 0, N) {
            while (A[i] > B[i]) {
                ll toPay = Y;
                if (!q1.empty()&&q1.top().cost+i*Z<Y) {
                    toPay = q1.top().cost + i*Z;
                    q1.pop();
                }
                ans += toPay;
                q2.push(Data{ -i*Z - toPay });
                A[i]--;
            }
            while(A[i]<B[i]) {
                ll toPay = X;
                if (!q2.empty() && q2.top().cost+i*Z<X) {
                    toPay = q2.top().cost + i*Z;
                    q2.pop();
                }
                ans += toPay;
                q1.push(Data{ -i*Z - toPay });
                A[i]++;
            }
        }
        out << ans << endl;
    }
    return 0;
}