#include <bits/stdc++.h>
using namespace std;



typedef unsigned long ul;
typedef unsigned long long ull;
typedef long long ll;
typedef vector<ll> vint;
typedef vector< vector<ll> > vvint;
typedef vector< vector< vector<ll> > > vvvint;
typedef vector<string> vstring;
typedef vector< vector<string> > vvstring;
typedef vector<char> vchar;
typedef vector< vector<char> > vvchar;
typedef vector<long double> vdouble;
typedef vector< vector<long double> > vvdouble;
typedef vector< vector< vector<long double> > > vvvdouble;
typedef pair<ll,ll> pint;
typedef vector<pint> vpint;
typedef vector<bool> vbool;

#define rep(i,n) for(ll i=0;i<n;i++)
#define repf(i,f,n) for(ll i=f;i<n;i++)
#define repr(i,n) for(ll i=n-1;i>=0;i--)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define ALL(obj) (obj).begin(), (obj).end()
// #define LLONG_MAX 9223372036854775806
#define vmax(vec) *max_element(vec.begin(), vec.end())
#define vmin(vec) *min_element(vec.begin(), vec.end())
#define vsort(vec) sort(vec.begin(), vec.end())
#define vsortgr(vec) sort(vec.begin(), vec.end(), greater<ll>())
#define MOD 1000000007
// #define MOD 998244353
// #define MOD LLONG_MAX
// const double PI=3.14159265358979323846;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }




int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0,};

template< typename T >
struct edge {
  int src, to;
  T cost;

  edge(int to, T cost) : src(-1), to(to), cost(cost) {}

  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  edge &operator=(const int &x) {
    to = x;
    return *this;
  }

  operator int() const { return to; }
};

template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedGraph = vector< Edges< T > >;
using UnWeightedGraph = vector< vector< int > >;
template< typename T >
using Matrix = vector< vector< T > >;

ll gcd(ll a, ll b)
{
    if (a < b) {
        a ^= b;
        b ^= a;
        a ^= b;
    }

    return b ? gcd(b, a % b) : a;
}

ll lcm(int a, ll b)
{
    return a * b / gcd(a, b);
}




// 繰り返し二乗法
ll power(ll a, ll b){
  if(a==1)return a;
  // if(a==0)re
  ll res=1;
  while(b>0){
    if(b&1) res=res*a%MOD;
    a=a*a%MOD;
    b>>=1;
  }
  return res;
}

const int MAX=1000000;

ll fact[MAX], fact_inv[MAX];

void init_fact(ll n){
  fact[0]=1;
  // 階乗の計算
  rep(i, n) fact[i+1]=fact[i]*(i+1)%MOD;
  fact_inv[n]=power(fact[n], MOD-2);
  // 逆元の計算
  for(ll i=n-1;i>=0;i--) fact_inv[i]=fact_inv[i+1]*(i+1)%MOD;
}

ll comb(ll n, ll r){
  return (fact[n]*fact_inv[r])%MOD*fact_inv[n-r]%MOD;
}

ll perm(ll n, ll r){
  return (fact[n]*fact_inv[n-r])%MOD;
}


// struct UnionFind {
//     vector<ll> par; // par[i]:iの親の番号　(例) par[3] = 2 : 3の親が2
//     vector<ll> num;
//     // vector<ll> dist; // rootまでの距離

//     UnionFind(ll N) : par(N), num(N){ //最初は全てが根であるとして初期化
//       for(ll i = 0; i < N; i++) par[i] = i;
//       for(ll i = 0; i < N; i++) num[i] = 1;
//       // for(ll i = 0; i < N; i++) dist[i] = 0;

//     }

//     ll root(ll x) { // データxが属する木の根を再帰で得る：root(x) = {xの木の根}
//         if (par[x] == x) return x;
//         return par[x] = root(par[x]);
//     }

//     void unite(ll x, ll y) { // xとyの木を併合
//         ll rx = root(x); //xの根をrx
//         ll ry = root(y); //yの根をry
//         if (rx == ry) return; //xとyの根が同じ(=同じ木にある)時はそのまま
//         par[rx] = ry; //xとyの根が同じでない(=同じ木にない)時：xの根rxをyの根ryにつける
//         num[ry] = num[rx] + num[ry];
//     }



//     bool same(ll x, ll y) { // 2つのデータx, yが属する木が同じならtrueを返す
//         ll rx = root(x);
//         ll ry = root(y);
//         return rx == ry;
//     }

//     ll size(ll x){
//       return num[root(x)];
//     }


// };

vint divisor(ll n){ // nの約数
  vint ret;
  for(ll i=1;i*i<=n;i++){
    if(n%i == 0){
      ret.pb(i);
      if(i*i!=n) ret.pb(n/i);
    }
  }
  vsort(ret);
  return ret;
}



ll get_digit_in(ll n, ll i){ // i桁目の数字を得る。
  for(ll j=0;j<i-1;j++){
    n/=10;
  }
  return n%10;
}

ll get_digit(ll n){
  ll rtn=0;
  while(n>0){
    n/=10;
    rtn++;
  }
  return rtn;
}

map<ll,ll> prime_factor(ll n){
  map<ll,ll> rtn;
  for(ll i=2;i*i<=n;i++){
    while(n%i == 0){
      rtn[i]++;
      n /= i;
    }
  }
  if(n!=1) rtn[n] = 1;
  return rtn;
}

// nPnの順列に対して処理を実行する
void foreach_permutation(ll n, function<void(ll *)> f) {
  ll indexes[n];
  for (ll i = 0; i < n; i++) indexes[i] = i;
  do {
    f(indexes);
  } while (std::next_permutation(indexes, indexes + n));
}

void recursive_comb(ll *indexes, ll s, ll rest, function<void(ll *)> f) {
  if (rest == 0) {
    f(indexes);
  } else {
    if (s < 0) return;
    recursive_comb(indexes, s - 1, rest, f);
    indexes[rest - 1] = s;
    recursive_comb(indexes, s - 1, rest - 1, f);
  }
}

// nCkの組み合わせに対して処理を実行する
void foreach_comb(ll n, ll k, function<void(ll *)> f) {
  ll indexes[k];
  recursive_comb(indexes, n - 1, k, f);
}

// nPkの順列に対して処理を実行する
void foreach_permutation(ll n, ll k, function<void(ll *)> f) {
  foreach_comb(n, k, [&](ll *c_indexes) {
    foreach_permutation(k, [&](ll *p_indexes) {
      ll indexes[k];
      for (ll i = 0; i < k; i++) {
        indexes[i] = c_indexes[p_indexes[i]];
      }
      f(indexes);
    });
  });
}



void printv(vint &V){
  for(auto e:V)cout<<e<<" ";
  cout<<endl;
}

template<typename T> class segtree {
private:
    int n,sz,h;
    vector<T> node, lazy;
    void eval(int k) {
        if(lazy[k]){
            node[k] += lazy[k];
            if(k < n) {
                lazy[k*2] += lazy[k] / 2, lazy[k*2+1] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }
 
public:
    segtree(const vector<T>& v) : sz((int)v.size()), h(0) {
        n = 1;
        while(n < sz) n *= 2, h++;
        node.resize(2*n, 0), lazy.resize(2*n, 0);
        for(int i = 0; i < sz; i++) node[i+n] = v[i];
        for(int i = n-1; i >= 1; i--) node[i] = node[2*i] + node[2*i+1];
    }
    void range(int a, int b, T x) {
        a += n, b += n - 1;
        for(int i = h; i > 0; i--) eval(a >> i), eval(b >> i);
        int ta = a, tb = b++, length = 1;
        while(a < b){
            if(a & 1) lazy[a++] += length * x;
            if(b & 1) lazy[--b] += length * x;
            a >>= 1, b >>= 1, length <<= 1;
        }
        while(ta >>= 1, tb >>= 1, ta){
            if(!lazy[ta]){
                eval(2*ta), eval(2*ta+1), node[ta] = node[2*ta] + node[2*ta+1];
            }
            if(!lazy[tb]){
                eval(2*tb), eval(2*tb+1), node[tb] = node[2*tb] + node[2*tb+1];
            }
        }
    }
    T query(int a, int b) {
        a += n, b += n - 1;
        for(int i = h; i > 0; i--) eval(a >> i), eval(b >> i);
        b++;
        T res1 = 0, res2 = 0;
        while(a < b) {
            if(a & 1) eval(a), res1 += node[a++];
            if(b & 1) eval(--b), res2 += node[b];
            a >>= 1, b >>= 1;
        }
        return res1 + res2;
    }
    void print(){for(int i = 0; i < sz; i++) cout<<query(i,i+1)<< " ";cout<<endl;}
};

int main() {


  cout<<fixed<<setprecision(10);

  // ll h,n; cin>>h>>n;
  // vint a(n),b(n); rep(i,n) cin>>a[i]>>b[i];

  // vvint dp(n+1, vint(h+1, -1));
  // dp[0][0] = 0;

  // rep(i,n){

  //   rep(j, a[i]){
  //     for(ll k=0; k*a[i]+j <= h; k++){
  //       if(dp[i][j])
  //     }
  //   }
  //   rep(j, h){
  //     if(dp[i+1][j] < 0) continue;
  //   }
  // }

  ll n,d,a; cin>>n>>d>>a;
  vint x(n),h(n); rep(i,n) cin>>x[i]>>h[i];
  vpint xh(n); rep(i,n) xh[i] = mp(x[i], h[i]);
  sort(ALL(xh));
  sort(ALL(x));
  rep(i,n){
    h[i] = xh[i].second;
  }

  auto tree = segtree<ll>(h);
  rep(i, n){
    tree.range(i,i, xh[i].second);
  }

  // tree.print();

  ll cur = xh[0].first;
  ll ans = 0;
  rep(i,n){
    ll cnt;
    ll hp = tree.query(i,i+1);
    cur = x[i];
    // cout<<hp<<endl;
    if(hp <= 0) continue;
    // if(i == 0) hp = xh[0].second;
    // else hp = tree.sum(i+1) - tree.sum(i);
    cnt = (hp+a-1)/a;
    ll j = upper_bound(x.begin(), x.end(), cur+2*d) - x.begin();
    // cout<<x[j]<<endl;
    // cout<<i<<" "<<j<<endl;
    tree.range(i,j, -cnt*a);
    ans += cnt;
    // tree.print();
  }

  cout<<ans<<endl;
}

//


Measured memory_bytes: 16768