//#pragma comment(linker,"/stack:200000000")
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#define si(x) scanf("%d",&x)
#define sii(a,b) scanf("%d%d",&a,&b)
#define siii(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define siiii(a,b,c,d) scanf("%d%d%d%d",&a,&b,&c,&d)
#define sl(x) scanf("%lld",&x)
#define sll(a,b) scanf("%lld%lld",&a,&b)
#define slll(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)
#define sllll(a,b,c,d) scanf("%lld%lld%lld%lld",&a,&b,&c,&d)
#define ss(x) scanf("%s",x+1)
#define pi(x) printf("%d",x)
#define pii(x,y) printf("%d %d",x,y)
#define piii(a,b,c) printf("%d %d %d",a,b,c)
#define piiii(a,b,c,d) printf("%d %d %d %d",a,b,c,d)
#define Pi(x) printf("%d\n",x)
#define Pii(x,y) printf("%d %d\n",x,y)
#define Piii(a,b,c) printf("%d %d %d\n",a,b,c)
#define Piiii(a,b,c,d) printf("%d %d %d %d\n",a,b,c,d)
#define pl(x) printf("%lld",x)
#define pll(x,y) printf("%lld %lld",x,y)
#define plll(a,b,c) printf("%lld %lld %lld",a,b,c)
#define pllll(a,b,c,d) printf("%lld %lld %lld %lld",a,b,c,d)
#define Pl(x) printf("%lld\n",x)
#define Pll(x,y) printf("%lld %lld\n",x,y)
#define Plll(a,b,c) printf("%lld %lld %lld\n",a,b,c)
#define Pllll(a,b,c,d) printf("%lld %lld %lld %lld\n",a,b,c,d)
#define ps(x) printf("%s",x+1)
#define space putchar(' ')
#define enter putchar('\n')
using namespace std;typedef long long LL;typedef long double LD;const LL pp=1e9+7;const LD eps=1e-8;
inline LL ksm(LL x,LL y=pp-2){x=(x%pp+pp)%pp;LL ans=1;while (y){if (y&1) ans=ans*x%pp;x=x*x%pp;y>>=1;}return ans;}
inline LL gcd(LL x,LL y){return y?gcd(y,x%y):x;}
inline void reads(char s[],int &n){n=0;char ch=getchar();while (ch==' ' || ch=='\n' || ch=='\r') ch=getchar();
while (ch!=' ' && ch!='\n' && ch!='\r' && ch!=EOF) s[++n]=ch,ch=getchar();}
 
// HEAP Attention : Int + Array_Size + Stores In key[] + Top.id/v = Min
// init() empty() top() push(id,value) pop()
/*
struct HEAP
{
    int sz;
    struct HEAP_Pair{int id,v;}T[100009];
    inline int ls(int x){return x<<1;}
    inline int rs(int x){return ((x<<1)|1);}
    inline int f(int x){return x>>1;} 
    inline void init(){sz=0;}
    inline bool empty(){return sz==0;}
    inline HEAP_Pair top(){return T[1];}
    inline void push(int x,int v)
    {
        T[++sz].id=x;
        T[sz].v=v;
        pushup(sz);
    }
    inline void pop()
    {
        T[1]=T[sz--];
        pushdown(1);
    }
    void pushup(int x)
    {
        if (x==1) return;
        if (T[x].v<T[f(x)].v)    //
        {
            HEAP_Pair tmp=T[f(x)];
            T[f(x)]=T[x];
            T[x]=tmp;
            pushup(f(x));
        }
    }
    void pushdown(int x)
    {
        if (ls(x)>sz) return;
        int t=ls(x);
        if (rs(x)<=sz)
            if (T[rs(x)].v<T[t].v) t=rs(x);   //
        if (T[t].v<T[x].v)   //
        {
            HEAP_Pair tmp=T[t];
            T[t]=T[x];
            T[x]=tmp;
            pushdown(t);
        }
    }
};*/

 
// BIT Attention : Bit.init(Size) + Int + Array_Size + [ add1(x,v) sum(l,r) ] Or [ add(l,r,v) get(x) ]
// init(Size) [ add1(x,v) sum(l,r) ] Or [ add(l,r,v) get(x) ]

struct BIT
{
	LL T[200009],sz;
	inline int lowbit(int x){return x&(-x);}
	inline void init(int x){sz=x;}
	inline void Badd(int x,LL v)
	{
		while (x<=sz)
		{
			T[x]+=v;
			x+=lowbit(x);
		}
	}
	inline LL Bsum(int x)
	{
		LL ans=0;
		while (x>=1)
		{
			ans+=T[x];
			x-=lowbit(x);
		}
		return ans;
	}
	inline void add1(int x,int v){Badd(x,v);}
	inline int sum(int l,int r){if (l>r) return 0;return Bsum(r)-Bsum(l-1);}
	inline void add(int l,int r,LL v){Badd(l,v);Badd(r+1,-v);}
	inline LL get(int x){return Bsum(x);}
}B;

 
//Min/Max Pri Que Attention : MPQ.init(Size,Type [0=Min;1=Max] ) + get().id/v/t + Int + Array_Size
//get().id/v/t push(id,value,time) init(Size,Type) upd(L,R) empty()
/*
struct MPQ
{
	int sz,l,r,type;
	struct MPQ_Pair{int id,v,t;}q[1000009];
	inline void init(int thesz,int thetype){sz=thesz;l=r=0;type=thetype;}
	inline bool empty(){return l==r;}
	inline int pre(int x){if (x-1<0) return sz;return x-1;}
	inline int suc(int x){if (x+1>sz) return 1;return x+1;}
	inline void push(int id,int v,int t)
	{
		if (!type)
			while (q[pre(r)].v>=v && !empty()) r=pre(r);
		else
			while (q[pre(r)].v<=v && !empty()) r=pre(r);
		q[r].id=id,q[r].v=v,q[r].t=t;
		r=suc(r);
	}
	inline MPQ_Pair get(){return q[l];}
	inline void upd(int tL,int tR){while ((q[l].t<tL || q[l].t>tR) && !empty()) l=suc(l);}
};
*/
//========================    C    ========================    N    ==================================
int n,L,R,MID;
LL w,a,ans,num,tot,lim;
struct ENEMY{LL x,h;}e[200009];
inline bool cmp(const ENEMY &a,const ENEMY &b){return a.x<b.x;}
int main()
{
	//freopen("r.txt","r",stdin);
	//freopen("w1.txt","w",stdout);
	si(n);sll(w,a);
	B.init(n);
	w=w*2ll+1ll;
	for (int i=1;i<=n;i++)
		sll(e[i].x,e[i].h);
	sort(e+1,e+n+1,cmp);
	for (int i=1;i<=n;i++)
	{
		e[i].h-=a*B.get(i);
		if (e[i].h<=0ll) continue;
		num=(e[i].h+a-1ll)/a;
		ans+=num;
		lim=e[i].x+w-1ll;
		L=1,R=n;
		while (L<R)
		{
			MID=(L+R+1)>>1;
			if (e[MID].x<=lim)
				L=MID;
			else
				R=MID-1;
		}
		if (e[L].x<=lim)
			B.add(i,L,num);
	}
	Pl(ans);
	return 0;
}

Measured memory_bytes: 4864