#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b) for(int i = a; i < b; i++)

#define min(a, b) ((a) < (b) ? (a) : (b))

#define max(a, b) ((a) > (b) ? (a) : (b))

#define index(a) (a - 'A')

#define transUpp(a) (a - 32)

#define transLow(a) (a + 32)

#define ll long long

#define PB push_back

int gcd(int a, int b){return b == 0 ? a : gcd(a%b, a);}

const int N = 782;

int y[N];

int main(int n, char**args)

{

    int apples, power, th, len, a, b, j = 1;

    cin >> apples >> power >> th >> len;

    y[0] = 0;

    for (int i = 1; i <= apples; i++)

    {

        cin >> a >> b;

        if (th + len >= a) // 够不着的不要

        {

            y[j] = b;

            int k = j - 1, w = y[j];

            while (k > 0 && w < y[k]) // 插排

            {

                y[k + 1] = y[k];

                k -= 1;

            }

            y[k + 1] = w;

            j += 1;

        }

    }

    n = 0;

    for (int i = 1; i < j; i++)

        if (power >= y[i])

            power -= y[i], n += 1;

    cout << n << endl;

    return 0;

}