#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <tuple>
#include <iomanip>
#include <climits>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
//typedef pair<ll, ll> P;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n)-1; i >= 0; i--)
#define pb push_back
#define f first
#define s second
#define chmin(x, y) x = min(x, y);
#define chmax(x, y) x = max(x, y);

//const ll INFL = LLONG_MAX;//10^18 = 2^60
const ll INFL = 1LL<<60;
//const int INF = INT_MAX;
const ll INF = 1 << 30;//10^9
ll MOD = 1000000007;
//ll MOD = 998244353;

vector<ll> dy = {0, 1, 0, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, 0, -1, 0, 1, -1, 1, -1, 0};

void pres(double A, ll x = 10){cout << fixed << setprecision(x) << A << endl;}
void BinarySay(ll x, ll y = 60){rep(i, y) cout << (x>>(y-1-i) & 1); cout << endl;}
ll cnt_bit(ll x){return __builtin_popcountll(x);}

ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x; k /= 2;
  }
  return res;
}

ll pow_mod(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}

ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll x, ll y){
  ll res = x / gcd(x, y);
  res *= y;
  return res;
};

//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}

const int MAXkai = 200010;
ll kai_memo[MAXkai];
ll kai(ll N){
  if(kai_memo[N] != 0) return kai_memo[N];
  if(N <= 1) return 1;
  return kai_memo[N] = N * kai(N-1) % MOD;
}


//区間加算区間和
const ll N_ = 1<<18;
ll seg[2 * N_ - 1], lazy[2 * N_ - 1];

void eval(ll k, ll l, ll r){
  if(lazy[k] == 0) return;
  seg[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(ll a, ll b, ll x, ll k = 0, ll l = 0, ll r = N_){
  eval(k, l, r);
  if(r <= a || b <= l) return;
  if(a <= l && r <= b){
    lazy[k] += (r - l) * x;
    eval(k, l, r);
    return;
  }
  add(a, b, x, 2 * k + 1, l, (l + r) / 2);
  add(a, b, x, 2 * k + 2, (l + r) / 2, r);
  seg[k] = seg[2 * k + 1] + seg[2 * k + 2];
  return;
}

ll getsum(ll a, ll b, ll k = 0, ll l = 0, ll r = N_){
  if(r <= a || b <= l) return 0;
  eval(k, l, r);
  if(a <= l && r <= b) return seg[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;
}

void solve(){
  ll N, D, A;
  cin >> N >> D >> A;
  vector<pair<ll, ll>> XH(N);
  rep(i, N) cin >> XH[i].f >> XH[i].s;
  sort(XH.begin(), XH.end());

  ll ans = 0;
  revrep(i, N){
    ll rest = XH[i].s;
    rest -= getsum(i, i + 1) * A;
    if(rest <= 0) continue;
    ll left = XH[i].f - 2 * D;
    ll ok = i, ng = -1;
    while(ok - ng > 1){
      ll mid = (ok + ng) / 2;
      if(left <= XH[mid].f){
        ok = mid;
      }else{
        ng = mid;
      }
    }
    ll need = (rest + A - 1) / A;
    ans += need;
    add(ok, i + 1, need);
  }
  cout << ans << endl;
}


int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}


Measured memory_bytes: 11136