import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.BufferedOutputStream;
import java.nio.charset.Charset;
import java.util.StringTokenizer;
import java.io.OutputStreamWriter;
import java.io.OutputStream;
import java.util.Collection;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UncheckedIOException;
import java.util.Objects;
import java.io.Writer;
import java.util.Queue;
import java.io.BufferedReader;
import java.util.Comparator;
import java.util.ArrayDeque;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author mikit
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        LightScanner in = new LightScanner(inputStream);
        LightWriter out = new LightWriter(outputStream);
        FSilverFoxVsMonster solver = new FSilverFoxVsMonster();
        solver.solve(1, in, out);
        out.close();
    }

    static class FSilverFoxVsMonster {
        public void solve(int testNumber, LightScanner in, LightWriter out) {
            // out.setBoolLabel(LightWriter.BoolLabel.YES_NO_FIRST_UP);
            int n = in.ints();
            long d = in.longs() * 2, a = in.longs();
            FSilverFoxVsMonster.Monster[] monsters = new FSilverFoxVsMonster.Monster[n];
            for (int i = 0; i < n; i++) {
                monsters[i] = new FSilverFoxVsMonster.Monster(in.longs(), (in.longs() + a - 1) / a);
            }
            IntroSort.sort(monsters, Comparator.comparing(monster -> monster.x));
            Queue<Vec2l> q = new ArrayDeque<>();
            long c = 0, ans = 0;
            for (int i = 0; i < n; i++) {
                while (!q.isEmpty() && q.peek().x < monsters[i].x) c -= q.poll().y;
                long r = Math.max(0, monsters[i].h - c);
                ans += r;
                c += r;
                q.offer(new Vec2l(monsters[i].x + d, r));
            }
            out.ans(ans).ln();
        }

        private static class Monster {
            long x;
            long h;

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

        }

    }

    static interface Verified {
    }

    static final class ArrayUtil {
        private ArrayUtil() {
        }

        public static <T> void swap(T[] a, int x, int y) {
            T t = a[x];
            a[x] = a[y];
            a[y] = t;
        }

    }

    static final class BitMath {
        private BitMath() {
        }

        public static int count(int v) {
            return Integer.bitCount(v);
        }

        public static int msb(int v) {
            if (v == 0) {
                throw new IllegalArgumentException("Bit not found");
            }
            v |= (v >> 1);
            v |= (v >> 2);
            v |= (v >> 4);
            v |= (v >> 8);
            v |= (v >> 16);
            return count(v) - 1;
        }

    }

    static class HeapSort {
        private HeapSort() {
        }

        private static <T> void heapfy(T[] a, int low, int high, int i, T val, Comparator<? super T> comparator) {
            int child = 2 * i - low + 1;
            while (child < high) {
                if (child + 1 < high && comparator.compare(a[child], a[child + 1]) < 0) {
                    child++;
                }
                if (comparator.compare(val, a[child]) >= 0) {
                    break;
                }
                a[i] = a[child];
                i = child;
                child = 2 * i - low + 1;
            }
            a[i] = val;
        }

        static <T> void sort(T[] a, int low, int high, Comparator<T> comparator) {
            for (int p = (high + low) / 2 - 1; p >= low; p--) {
                heapfy(a, low, high, p, a[p], comparator);
            }
            while (high > low) {
                high--;
                T pval = a[high];
                a[high] = a[low];
                heapfy(a, low, high, low, pval, comparator);
            }
        }

    }

    static class InsertionSort {
        private InsertionSort() {
        }

        static <T> void sort(T[] a, int low, int high, Comparator<? super T> comparator) {
            for (int i = low; i < high; i++) {
                for (int j = i; j > low && comparator.compare(a[j - 1], a[j]) > 0; j--) {
                    ArrayUtil.swap(a, j - 1, j);
                }
            }
        }

    }

    static class Vec2l implements Comparable<Vec2l> {
        public long x;
        public long y;

        public Vec2l(long x, long y) {
            this.x = x;
            this.y = y;
        }

        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Vec2l vec2i = (Vec2l) o;
            return x == vec2i.x &&
                    y == vec2i.y;
        }

        public int hashCode() {
            return Objects.hash(x, y);
        }

        public String toString() {
            return "(" + x + ", " + y + ")";
        }

        public int compareTo(Vec2l o) {
            if (x == o.x) {
                return Long.compare(y, o.y);
            }
            return Long.compare(x, o.x);
        }

        public Vec2l clone() throws CloneNotSupportedException {
            return (Vec2l) super.clone();
        }

    }

    static class IntroSort {
        private static int INSERTIONSORT_THRESHOLD = 16;

        private IntroSort() {
        }

        static <T> void sort(T[] a, int low, int high, int maxDepth, Comparator<T> comparator) {
            while (high - low > INSERTIONSORT_THRESHOLD) {
                if (maxDepth-- == 0) {
                    HeapSort.sort(a, low, high, comparator);
                    return;
                }
                int cut = QuickSort.step(a, low, high, comparator);
                sort(a, cut, high, maxDepth, comparator);
                high = cut;
            }
            InsertionSort.sort(a, low, high, comparator);
        }

        public static <T> void sort(T[] a, Comparator<T> comparator) {
            if (a.length <= INSERTIONSORT_THRESHOLD) {
                InsertionSort.sort(a, 0, a.length, comparator);
            } else {
                sort(a, 0, a.length, 2 * BitMath.msb(a.length), comparator);
            }
        }

    }

    static class QuickSort {
        private QuickSort() {
        }

        private static <T> void med(T[] a, int low, int x, int y, int z, Comparator<? super T> comparator) {
            if (comparator.compare(a[z], a[x]) < 0) {
                ArrayUtil.swap(a, low, x);
            } else if (comparator.compare(a[y], a[z]) < 0) {
                ArrayUtil.swap(a, low, y);
            } else {
                ArrayUtil.swap(a, low, z);
            }
        }

        static <T> int step(T[] a, int low, int high, Comparator<? super T> comparator) {
            int x = low + 1, y = low + (high - low) / 2, z = high - 1;
            if (comparator.compare(a[x], a[y]) < 0) {
                med(a, low, x, y, z, comparator);
            } else {
                med(a, low, y, x, z, comparator);
            }

            int lb = low + 1, ub = high;
            while (true) {
                while (comparator.compare(a[lb], a[low]) < 0) {
                    lb++;
                }
                ub--;
                while (comparator.compare(a[low], a[ub]) < 0) {
                    ub--;
                }
                if (lb >= ub) {
                    return lb;
                }
                ArrayUtil.swap(a, lb, ub);
                lb++;
            }
        }

    }

    static class LightScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public LightScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
        }

        public String string() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int ints() {
            return Integer.parseInt(string());
        }

        public long longs() {
            return Long.parseLong(string());
        }

    }

    static class LightWriter implements AutoCloseable {
        private final Writer out;
        private boolean autoflush = false;
        private boolean breaked = true;

        public LightWriter(Writer out) {
            this.out = out;
        }

        public LightWriter(OutputStream out) {
            this(new OutputStreamWriter(new BufferedOutputStream(out), Charset.defaultCharset()));
        }

        public LightWriter print(char c) {
            try {
                out.write(c);
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter print(String s) {
            try {
                out.write(s, 0, s.length());
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter ans(String s) {
            if (!breaked) {
                print(' ');
            }
            return print(s);
        }

        public LightWriter ans(long l) {
            return ans(Long.toString(l));
        }

        public LightWriter ln() {
            print(System.lineSeparator());
            breaked = true;
            if (autoflush) {
                try {
                    out.flush();
                } catch (IOException ex) {
                    throw new UncheckedIOException(ex);
                }
            }
            return this;
        }

        public void close() {
            try {
                out.close();
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
        }

    }
}



Measured memory_bytes: 105432