#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp>  
#include <functional>
#include <iostream> 
#include<bits/stdc++.h>
using namespace __gnu_pbds;  
using namespace std;  
// Declaring ordered_set 
typedef tree<long long int, null_type, less<long long int>, rb_tree_tag,  
            tree_order_statistics_node_update>  
    ordered_set;  
typedef pair<long long int,long long int> pa;
#define resize(A) A.resize(unique(A.begin(), A.end()) - A.begin())
#define pb push_back
#define  MAX 200005
long long int MOD=998244353;
long long int mod=1e9+7;
long long int INF=1e18;
 
///////////////////////////////////////////////sieve////////////////////////////////////////////////////////////////////
/* bool B[MAX];
 // long long int C[MAX]={0};
  vector<long long int>V1;
 void sieve()
 {
    long long int i,j;
    for(i=2;i<MAX;i++)
    {
      if(!B[i])
     { 
         
        for(j=2*i;j<MAX;j=j+i)
        {
            B[j]=true;
          //  C[j]=max(C[j],i);
        }
      }
    }
 }
 
 
 */
 
//////////////////////////////////////////////////////////D-S-U/////////////////////////////////////////////////////////
/*long long int parent[MAX];
long long int size[MAX];
void initialise()
{ //cout<<MAX<<" ";
    for(long  long int i=0;i<MAX;i++)
    {
        parent[i]=i;
        //cout<<i<<" ";
        size[i]=1;
    }
}
long long int  root(long long int x)
{
    while(x!=parent[x])
    {
        parent[x]=parent[parent[x]];
        x=parent[x];
    }
    return x;
}
 
    
void union1(long long int x,long long int y)
{
    if(size[x]>=size[y])
    {
        size[x]+=size[y];
        parent[y]=x;
        
    }
    else
    {
        size[y]+=size[x];
        parent[x]=y;
    }
}*/
//////////////////////////////////////////////////////MODPOWER//////////////////////////////////////////////////////////
 
 
/*long long int modulo(long long int a,long long  int b, long long int n){
    long long int  x=1, y=a%n; 
    while (b > 0) {
        if (b%2 == 1) {
            x = (x*y) % n; // multiplying with base
        }
        y = (y*y) % n; // squaring the base
        b /= 2;
    }
    return x % n;
}
*/
 
 
 
////////////////////////////////////////////////BIT/////////////////////////////////////////////////////////////////////
/* long long int bit[MAX+1]={0};
long long int sum(long long int in,long long int n)
{
    //in=in+1;
    long long int sum=0;
    if(in==0)
        return 0;
    while(in>0)
    {
      sum=sum+bit[in];
        
        in=in-(in&(-in));
    }
    return sum;
}
void update(long long int in,long long int n,long long int val)
{
    // in=in+1;
    
    while(in<=n)
    {
       // cout<<in<<" ";
        bit[in]+=val;
        in=in+ (in &(-in));
    }
}
*/
/*long long int dist[107][107];
long long int parent[101];
long long int size[101]
void initialise()
{ //cout<<MAX<<" ";
    for(long  long int i=0;i<101;i++)
    {
        parent[i]=i;
        size[i]=1;
    }
}
long long int  root(long long int x)
{
    while(x!=parent[x])
    {
        parent[x]=parent[parent[x]];
        x=parent[x];
    }
    return x;
}
 
    
void union1(long long int x,long long int y)
{
    if(size[x]>=size[y])
    {
        size[x]+=size[y];
        parent[y]=x;
    }
    else
    {
        size[y]+=size[x];
        parent[x]=y;
    }
}
long long int kr(pair<long long int,pair<long long int ,long long int>>p[],long long int e)
{long long int i;
 long long int cost=0;
    for(i=0;i<e;i++)
    { 
        long long int x=p[i].second.first;
        long long int y=p[i].second.second;
        long long c=p[i].first;
        if(root(x)!=root(y))
        {     cost=cost+c;
            union1(root(x),root(y));
        }
    }
 return cost;
}*/

int main()
{
ios_base::sync_with_stdio(false); 
cin.tie(NULL);
cout.tie(NULL);
long long int c,d,i,w,j,k=0,l=0,r=0,m=0,n,p,cnt=0,cnt1=0,x,y=0,z=0,a,b,low,mid,high,ans=0,maxi=0,mini=INF,t1,x1,y1,t,o;
string s,s1;    long long qt,xx;        char jj;
cin>>n>>d>>a;
    vector<pa>V;
    for(i=0;i<n;i++)
    {
        cin>>x>>y;
        V.pb({x,y});
    }
    long long int C[n+1]={0};
    sort(V.begin(),V.end());
   
    
    r=0;
    for(i=0;i<V.size();i++)
    {
        
        
        l=V[i].first+d;
        r=r+C[i];
        V[i].second=V[i].second-r;
        if(V[i].second<0)
            continue;
        
        p=V[i].second/a;
        if(((V[i].second)%a)!=0)
            p++;
        
        cnt+=p;
       
        low=i+1;
        high=n-1;
        ans=i;
        while(low<=high)
        {
            mid=(low+high)/2;
            if(V[mid].first<=l+d)
            {
                low=mid+1;
                ans=max(ans,mid);
            }
            else
            {
                high=mid-1;
            }
            
        }
        r=r+p*a;
        C[ans+1]-=p*a;
        
    }
    cout<<cnt<<endl;
    
    

}


Measured memory_bytes: 6384