#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int n, m, c, p;
    std::cin >> n >> m >> c >> p;
    
    std::vector<i64> a;
    i64 sum = 0;
    for (int i = 0; i < n + m; i++) {
        int t, h;
        std::cin >> t >> h;
        
        if (t == 1) {
            sum += h;
        } else {
            a.push_back(sum + h);
        }
    }
    std::sort(a.begin(), a.end());
    
    i64 ans = 0;
    for (int i = 1; i <= a.size(); i++) {
        ans = std::max(ans, 1LL * i * p - 1LL * c * (a[i - 1] - 1));
    }
    std::cout << ans << "\n";
    
    return 0;
}