import java.util.Arrays;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Comparator;
import java.util.InputMismatchException;
import java.io.InputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.PriorityQueue;

public class Main {
    InputStream is;

    int __t__ = 1;
    int __f__ = 0;
    int __FILE_DEBUG_FLAG__ = __f__;
    String __DEBUG_FILE_NAME__ = "src/F1";

    FastScanner in;
    PrintWriter out;

    class Monster {
        final long x;
        final long h;

        public Monster(long x, long h) {
            this.x = x;
            this.h = h;
        }
    }

    class Event {
        final int t;
        final long x;
        final long cnt;

        public Event(int t, long x, long cnt) {
            this.t = t;
            this.x = x;
            this.cnt = cnt;
        }
    }

    public void solve() {
        int N = in.nextInt();
        long D = in.nextInt(), A = in.nextInt();
        Monster[] ms = new Monster[N];
        for (int i = 0; i < N; i++) {
            long x = in.nextInt();
            long h = in.nextInt();
            ms[i] = new Monster(x, h);
        }

        PriorityQueue<Event> pq = new PriorityQueue<>((e1, e2) -> {
            if (e1.x != e2.x) {
                return Long.compare(e1.x, e2.x);
            } else {
                return Integer.compare(e1.t, e2.t);
            }
        });

        for (int i = 0; i < N; i++) {
            pq.add(new Event(0, ms[i].x, (ms[i].h + A - 1) / A));
        }

        long cur = 0;
        long res = 0;
        while (!pq.isEmpty()) {
            Event e = pq.poll();
            if (e.t == 0) {
                if (e.cnt - cur > 0) {
                    pq.add(new Event(1, e.x + 2 * D, e.cnt - cur));
                    res += e.cnt - cur;
                    cur = e.cnt;
                }
            } else {
                cur -= e.cnt;
            }
        }
        System.out.println(res);
    }

    public void run() {
        if (__FILE_DEBUG_FLAG__ == __t__) {
            try {
                is = new FileInputStream(__DEBUG_FILE_NAME__);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            System.out.println("FILE_INPUT!");
        } else {
            is = System.in;
        }
        in = new FastScanner(is);
        out = new PrintWriter(System.out);

        solve();
    }

    public static void main(final String[] args) {
        new Main().run();
    }
}


class FastScanner {
    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;

    public FastScanner(InputStream stream) {
        this.stream = stream;
        // stream = new FileInputStream(new File("dec.in"));
    }

    int read() {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars) {
            curChar = 0;
            try {
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }

    public boolean isSpaceChar(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    public boolean isEndline(int c) {
        return c == '\n' || c == '\r' || c == -1;
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public int[] nextIntArray(int n) {
        int[] array = new int[n];
        for (int i = 0; i < n; i++)
            array[i] = nextInt();

        return array;
    }

    public int[][] nextIntMap(int n, int m) {
        int[][] map = new int[n][m];
        for (int i = 0; i < n; i++) {
            map[i] = nextIntArray(m);
        }
        return map;
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

    public long[] nextLongArray(int n) {
        long[] array = new long[n];
        for (int i = 0; i < n; i++)
            array[i] = nextLong();

        return array;
    }

    public long[][] nextLongMap(int n, int m) {
        long[][] map = new long[n][m];
        for (int i = 0; i < n; i++) {
            map[i] = nextLongArray(m);
        }
        return map;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }

    public double[] nextDoubleArray(int n) {
        double[] array = new double[n];
        for (int i = 0; i < n; i++)
            array[i] = nextDouble();

        return array;
    }

    public double[][] nextDoubleMap(int n, int m) {
        double[][] map = new double[n][m];
        for (int i = 0; i < n; i++) {
            map[i] = nextDoubleArray(m);
        }
        return map;
    }

    public String next() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do {
            res.appendCodePoint(c);
            c = read();
        } while (!isSpaceChar(c));
        return res.toString();
    }

    public String[] nextStringArray(int n) {
        String[] array = new String[n];
        for (int i = 0; i < n; i++)
            array[i] = next();

        return array;
    }

    public String nextLine() {
        int c = read();
        while (isEndline(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do {
            res.appendCodePoint(c);
            c = read();
        } while (!isEndline(c));
        return res.toString();
    }

    public int[][] nextPackedIntArrays(int packN, int size) {
        int[][] res = new int[packN][size];
        for (int i = 0; i < size; i++) {
            for (int j = 0; j < packN; j++) {
                res[j][i] = nextInt();
            }
        }
        return res;
    }
}


Measured memory_bytes: 67940