#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];
bitset<N> L[N], R[N];

bool in_side(int x0, int y0, int r, int a, int b) {
    if (b <= y0)return true;
    int dx = x0 - a;
    int dy = y0 - b;

    return 1ll * dx * dx + 1ll * dy * dy <= 1ll * r * r;
}

ll dp[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++) {
        int j = i;
        while (j < n) {
            j++;
            int x0 = x[i] + x[j];            // (xi + xj) / 2
            int y0 = 2 * h - (x[j] - x[i]);  // h - (xj - xi) / 2
            if (!in_side(x0, y0, x[j] - x[i], x[j] * 2, y[j] * 2))break;
            L[i][j] = 1;
        }
    }
    for (int i = n; i >= 1; i--) {
        int j = i;
        while (j) {
            j--;
            int x0 = x[i] + x[j];            // (xi + xj) / 2
            int y0 = 2 * h - (x[i] - x[j]);  // h - (xj - xi) / 2
            if (!in_side(x0, y0, x[i] - x[j], x[i] * 2, y[i] * 2))break;
            R[j][i] = 1;
        }
    }
    dp[1] = 1ll * (h - y[1]) * a;
    for (int i = 2; i <= n; i++) {
        dp[i] = 1e18;
        int bst = 1;
        for (int j = 1; j < i; j++) {
            if (L[j][i] && R[j][i]) {
                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[i] == dp[j - 1] + cost) bst = j;
            }
        }
    }
    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();
    }
}