#include<iostream>
#include <bits/stdc++.h>


#define ld long double
#define ll long long
#define IO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

using namespace std;

const int N = 1e4 + 2, MOD = 998244353;

int x[N], y[N];


ll dp[N];
ld L[N], R[N];

void doWork() {
    int n, h, a, b;
    cin >> n >> h >> a >> b;
    for (int i = 1; i <= n; i++) {
        cin >> x[i] >> y[i];
    }
    for (int i = 1; i <= n; i++) {
        L[i] = 1e9;
        int j = i;
        while (j <= n && x[j] <= x[i] + L[i]) {
            int c1 = x[j] - x[i], c2 = y[j] - h;
            ll B = 2 * (c2 - c1), C = 1ll * c1 * c1 + 1ll * c2 * c2;
            ld r = (-B + sqrt(B * B - 4 * C)) / 2;
//            cout<<c1<<" "<<c2<<"\n";
//            cout << B << " " << C << "\n";
//            cout << i << " " << j << " " << r << "\n";
            r = max(r, (ld) h - y[j]);
            L[i] = min(L[i], r);
            j++;
        }
        R[i] = 1e9;
        j = i ;
        while (j && x[j] >= x[i] - R[i]) {
            int c1 = x[j] - x[i], c2 = y[j] - h;
            ll B = 2 * (c1 + c2), C = 1ll * c1 * c1 + 1ll * c2 * c2;
            ld r = (-B + sqrt(B * B - 4 * C)) / 2;
            r = max(r, (ld) h - y[j]);
            R[i] = min(R[i], r);
            j--;
        }
//        cout << L[i] << " " << R[i] << "\n";
    }
    dp[1] = 1ll * (h - y[1]) * a;
    for (int i = 2; i <= n; i++) {
        dp[i] = 1e18;
        for (int j = 1; j < i; j++) {
            if (L[j] + R[i] >= x[i] - x[j]) {
                ll cost = 1ll * (h - y[i]) * a;
                ll d = x[i] - x[j];
                cost += 1ll * d * d * b;
                dp[i] = min(dp[i], dp[j] + cost);
            }
        }
    }
    if (dp[n] < 1e18) {
        cout << dp[n];
    } else {
        cout << "impossible";
    }
}

int main() {

    IO
    int t = 1;
//    cin >> t;
    for (int i = 1; i <= t; i++) {
        //  cout << "Case #" << i << ": ";
        doWork();
    }
}