#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<P, ll> T;
 
long long int INF = 1e17;
const ll fact_table = 800008;
double Pi = 3.1415926535897932384626;

priority_queue <ll> pql;
priority_queue <P> pqp;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
// priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
ll dx[8]={1,0,-1,0,1,1,-1,-1};
ll dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//↓,→,↑,←
 
 
#define p(x) cout<<x<<"\n";
#define el cout<<endl;
#define pe(x) cout<<(x)<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
// #define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
#define pc(x) cout << x << ",";
 
 
//ll mod = 998244353;
ll mod = 1000000007;
 
ll rui(ll number1,ll number2){
 
    if(number2 == 0){
        return 1;
    }else{
        ll number3 = rui(number1,number2 / 2);
        number3 *= number3;
        number3 %= mod;
        if(number2%2==1){
            number3 *= number1;
            number3 %= mod;
        }
        return number3;
    }
}
ll gcd(ll number1,ll number2){
 
    if(number1 > number2){
        swap(number1,number2);
    }
    if(number1 == 0 || number1 == number2){
        return number2;
    }else{
        return gcd(number2 % number1,number1);
    }
}
void YES(bool condition){
 
    if(condition){
        p("YES");
    }else{
        p("NO");
    }
    return;
}
void Yes(bool condition){
 
    if(condition){
        p("Yes");
    }else{
        p("No");
    }
    return;
}
 
/*
ll fact[fact_table + 5],rfact[fact_table + 5];
 
void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=fact_table; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[fact_table] = rui(fact[fact_table],mod - 2);
    for(ll i=fact_table; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod ) * rfact[n-r]) % mod;}
*/
 
ll n,m,num,sum,ans,a,b,c,d,e,h,r,l,q;
ll k;
ll x[500005], y[500005], z[500005];
char s[500005], t[500005];
P table[500005];

struct LazySegmentTree {
private:
    int n;
    vector<ll> node, lazy;
 
public:
    LazySegmentTree(vector<ll> v) {
        int sz = (int)v.size();
        n = 1; while(n < sz) n *= 2;
        node.resize(2*n-1);
        lazy.resize(2*n-1, 0);
 
        for(int i=0; i<sz; i++) node[i+n-1] = v[i];
        for(int i=n-2; i>=0; i--) node[i] = node[i*2+1] + node[i*2+2];
    }
 
    void eval(int k, int l, int r) {
        if(lazy[k] != 0) {
            node[k] += lazy[k];
            if(r - l > 1) {
                lazy[2*k+1] += lazy[k] / 2;
                lazy[2*k+2] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }
 
    void add(int a, int b, ll x, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        eval(k, l, r);
        if(b <= l || r <= a) return;
        if(a <= l && r <= b) {
            lazy[k] += (r - l) * x;
            eval(k, l, r);
        }
        else {
            add(a, b, x, 2*k+1, l, (l+r)/2);
            add(a, b, x, 2*k+2, (l+r)/2, r);
            node[k] = node[2*k+1] + node[2*k+2];
        }
    }
 
    ll getsum(int a, int b, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        eval(k, l, r);
        if(b <= l || r <= a) return 0;
        if(a <= l && r <= b) return node[k];
        ll vl = getsum(a, b, 2*k+1, l, (l+r)/2);
        ll vr = getsum(a, b, 2*k+2, (l+r)/2, r);
        return vl + vr;
    }
};

LazySegmentTree seg(vector<ll> (200010, 0));

void attack(ll damage, ll l, ll r){
    // [l, r]にダメージを与える
    ll ok = n, ng = -1;
    while(ok - ng > 1){
        ll mid = (ok + ng) / 2;
        if(table[mid].first >= l){
            ok = mid;
        }else{
            ng = mid;
        }
    }
    if(ok == n)return;
    ll lidx = ok;
    ok = -1, ng = n;
    while(ng - ok > 1){
        ll mid = (ok + ng) / 2;
        if(table[mid].first <= r){
            ok = mid;
        }else{
            ng = mid;
        }
    }
    if(ok == -1)return;
    ll ridx = ok;
    if(ridx < lidx)return;
    seg.add(lidx, ridx + 1, -damage);
}

ll myhp(ll idx){
    return seg.getsum(idx, idx + 1);
}

int main(){
    cin >> n >> d >> a;
    for(ll i=0;i<n;i++){
        cin >> x[i] >> y[i];
        table[i].first = x[i];
        table[i].second =  y[i];
    }
    sort(table, table + n);
    for(ll i=0;i<n;i++){
        seg.add(i, i + 1, table[i].second);
    }
    for(ll i=0;i<n;i++){
        ll hp = myhp(i);
        if(hp < 0)continue;
        ll times = (hp + a - 1) / a;
        ans += times;
        attack(times * a, table[i].first, table[i].first + 2 * d);
    }
    p(ans);

    return 0;
}


















Measured memory_bytes: 16612