#include<bits/stdc++.h>
using namespace std;
#define rep(i,x,y) for(int i=x;i<y;i++)
#define range(a) (a).begin(),(a).end()
#define print(A,x,n) rep(i,0,n){cout<<(i ? " ":"")<<A[i]x;}cout<<endl;
#define pprint(A,y,m,n) rep(j,0,m){print(A[j],y,n);}
const long mod=1e9+7;
const int size=1e5;
const int inf=1e9;
int main(){
	int N;long D,A;cin>>N>>D>>A;
	pair<long,long> X[N];
	rep(i,0,N) cin>>X[i].first>>X[i].second;
	sort(X,X+N);
	long t[N];long res=0;
	long ans=0;
	int j=0;
	rep(i,0,N){
		while(X[j].first+2*D<X[i].first){
			res-=t[j];
			j++;
		}
        X[i].second-=res*A;
		t[i]=max((X[i].second+A-1)/A,(long)0);
		res+=t[i]; ans+=t[i];
		X[i].second-=A*t[i];
	}
	cout<<ans<<endl;
}