package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
)

func main() {
	data, _ := io.ReadAll(os.Stdin)
	idx := 0
	nextInt := func() int64 {
		n := len(data)
		for idx < n && (data[idx] < '0' || data[idx] > '9') && data[idx] != '-' {
			idx++
		}
		sign := int64(1)
		if idx < n && data[idx] == '-' {
			sign = -1
			idx++
		}
		var val int64
		for idx < n && data[idx] >= '0' && data[idx] <= '9' {
			val = val*10 + int64(data[idx]-'0')
			idx++
		}
		return val * sign
	}

	_ = nextInt()
	n := int(nextInt())
	p := nextInt()
	t := nextInt()

	var ans int64
	var lastEnd int64
	hasSong := false

	for i := 0; i < n; i++ {
		l := nextInt()
		r := nextInt()

		if !hasSong {
			if r-l >= p {
				cnt := (r - l) / p
				ans += cnt
				lastEnd = l + cnt*p
				hasSong = true
			}
			continue
		}

		start := l
		need := lastEnd + t
		if start < need {
			start = need
		}

		if r-start >= p {
			cnt := (r - start) / p
			ans += cnt
			lastEnd = start + cnt*p
		}
	}

	out := bufio.NewWriter(os.Stdout)
	fmt.Fprint(out, ans)
	out.Flush()
}