import java.util.*; import java.io.*; import java.math.*;
public class Main{
	//Don't have to see. start------------------------------------------
	static class InputIterator{
		ArrayList<String> inputLine = new ArrayList<String>(1024);
		int index = 0; int max; String read;
		InputIterator(){
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			try{
				while((read = br.readLine()) != null){
					inputLine.add(read);
				}
			}catch(IOException e){}
			max = inputLine.size();
		}
		boolean hasNext(){return (index < max);}
		String next(){
			if(hasNext()){
				return inputLine.get(index++);
			}else{
				throw new IndexOutOfBoundsException("There is no more input");
			}
		}
	}
	static HashMap<Integer, String> CONVSTR = new HashMap<Integer, String>();
	static InputIterator ii = new InputIterator();//This class cannot be used in reactive problem.
	static PrintWriter out = new PrintWriter(System.out);
	static void flush(){out.flush();}
	static void myout(Object t){out.println(t);}
	static void myerr(Object t){System.err.print("debug:");System.err.println(t);}
	static String next(){return ii.next();}
	static boolean hasNext(){return ii.hasNext();}
	static int nextInt(){return Integer.parseInt(next());}
	static long nextLong(){return Long.parseLong(next());}
	static double nextDouble(){return Double.parseDouble(next());}
	static ArrayList<String> nextStrArray(){return myconv(next(), 8);}
	static ArrayList<String> nextCharArray(){return myconv(next(), 0);}
	static ArrayList<Integer> nextIntArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Integer> ret = new ArrayList<Integer>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Integer.parseInt(input.get(i)));
		}
		return ret;
	}
	static ArrayList<Long> nextLongArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Long> ret = new ArrayList<Long>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Long.parseLong(input.get(i)));
		}
		return ret;
	}
	static String myconv(Object list, int no){//only join
		String joinString = CONVSTR.get(no);
		if(list instanceof String[]){
			return String.join(joinString, (String[])list);
		}else if(list instanceof ArrayList){
			return String.join(joinString, (ArrayList)list);
		}else{
			throw new ClassCastException("Don't join");
		}
	}
	static ArrayList<String> myconv(String str, int no){//only split
		String splitString = CONVSTR.get(no);
		return new ArrayList<String>(Arrays.asList(str.split(splitString)));
	}
	public static void main(String[] args){
		CONVSTR.put(8, " "); CONVSTR.put(9, "\n"); CONVSTR.put(0, "");
		solve();flush();
	}
	//Don't have to see. end------------------------------------------
	static void solve(){//Here is the main function
		ArrayList<Integer> one = nextIntArray();
		int N = one.get(0);
		int D = one.get(1);
		int A = one.get(2);
		Node[] list = new Node[N];
		for(int i = 0; i < N; i++){
			ArrayList<Integer> tmp = nextIntArray();
			list[i] = new Node(tmp.get(0), tmp.get(1));
		}
		Arrays.sort(list, new originComparator());
		long output = 0;
		long sum = 0;
		ArrayDeque<QueueObject> queue = new ArrayDeque<QueueObject>();
		for(int i = 0; i < N; i++){
			int x = list[i].x;
			long h = list[i].h;
			while(queue.size() > 0){
				QueueObject first = queue.peekFirst();
				int nx = first.nx;
				if(nx < x){
					sum -= first.at;
					queue.pollFirst();
				}else{
					break;
				}
			}
			h -= sum;
			if(h > 0){
				long attack = (h + A - 1) / A;
				output += attack;
				sum += attack * A;
				queue.add(new QueueObject(x + D * 2, attack * A));
			}
		}
		myout(output);
	}
	//Method addition frame start

static class Node{
	int x;
	int h;
	Node(int x, int h){
		this.x = x;
		this.h = h;
	}
}

static class originComparator implements Comparator<Node>{
	public int compare(Node mae, Node ato){
		return mae.x - ato.x;
	}
}

static class QueueObject{
	int nx;
	long at;
	QueueObject(int nx, long at){
		this.nx = nx;
		this.at = at;
	}
}


	//Method addition frame end
}


Measured memory_bytes: 77396