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

#define NDEBUG
#include <cassert>


typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<llll> vllll;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define eb  emplace_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define repC3(vari,varj,vark,n)  for(int vari=0;vari<(n)-2;++vari)for(int varj=vari+1;varj<(n)-1;++varj)for(int vark=varj+1;vark<(n);++vark)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair
#define clamp(v,lo,hi) min(max(v,lo),hi)

template <typename T>
inline bool found(set<T> &s, T elem) { return s.find(elem) != s.end(); }
template <typename T>
inline bool found(unordered_set<T> &s, T elem) { return s.find(elem) != s.end(); }
template <typename T, typename U>
inline bool found(map<T,U> &s, U elem) { return s.find(elem) != s.end(); }
template <typename T, typename U>
inline bool found(unordered_map<T,U> &s, U elem) { return s.find(elem) != s.end(); }
template <typename T>
inline bool found(vector<T> &s, T elem) { return find(s.begin(), s.end(), elem) != s.end(); }
inline int found(string &s, string t) { return (int)s.find(t); }
inline int found(string &s, int c) { return (int)s.find(c); }

template<typename T1, typename T2> inline void amin(T1 & a, T2 const & b) { if (a>b) a=b; }
template<typename T1, typename T2> inline void amax(T1 & a, T2 const & b) { if (a<b) a=b; }
template<typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template<typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }

inline ll square(ll x) { return x * x; }
inline ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }
template <typename T>
inline T mod(T a, T b) { return ((a % b) + b) % b; }

template <typename T>
int find_left(vector<T>& v, T elem) {
    return (int)(upper_bound(v.begin(), v.end(), elem) - v.begin()) - 1;
}
template <typename T>
int find_right(vector<T>& v, T elem) {
    return (int)(lower_bound(v.begin(), v.end(), elem) - v.begin());
}

const ll MOD=1000000007LL;

ll ADD(ll x, ll y) { return (x+y) % MOD; }
ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
ll MUL(ll x, ll y) { return x*y % MOD; }
ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
ll DIV(ll x, ll y) { /*assert(y%MOD!=0);*/ return MUL(x, POW(y, MOD-2)); }

#define INTSPACE 12
char _buf[INTSPACE*1000000 + 3];

int loadint() {
    if (fgets(_buf, INTSPACE+3, stdin)==NULL) return 0;
    return atoi(_buf);
}

int loadvec(vector<int>& v, int N=-1) {
    if (N == 0) {
        v.clear();
        return 0;
    }
    if (N == -1) {
        N = loadint();
        if (N==0) return 0;
    }
    int bufsize = INTSPACE*N + 3;
    if (fgets(_buf, bufsize, stdin)==NULL) return 0;
    v.resize(N);

    int i=0;
    bool last = false;
    for (char *p=&_buf[0]; ;) {
        char *q = p;
        while (*q > ' ') ++q;
        if (*q == 0x0D || *q == 0x0A) last = true;
        *q = 0;
        v[i++] = atoi(p);
        if (last || i == N) break;
        p = q+1;
    }
    return i;
}
void read_cr() {
    fgets(_buf, 256, stdin);
}


template <typename Elem, typename LazyOperand>
class LazySegmentTree {
 public:
    Elem (*f)(Elem a, Elem b);
    Elem (*g)(Elem a, LazyOperand b);
    LazyOperand (*h)(LazyOperand a, LazyOperand b);
    using fTYPE = decltype(f);
    using gTYPE = decltype(g);
    using hTYPE = decltype(h);

    Elem elem_ident;
    LazyOperand lazy_operand_ident;
    vector<Elem> elems;
    vector<LazyOperand> lazy_operands;
    int n, height;

    LazySegmentTree(fTYPE f, gTYPE g, hTYPE h,
                    Elem elem_ident, LazyOperand lazy_operand_ident)
        : f(f), g(g), h(h),
          elem_ident(elem_ident), lazy_operand_ident(lazy_operand_ident) {}

    void init(int n_temp) {
        n = 1; height = 0;
        while (n < n_temp) { n <<= 1; ++height; }
        elems.assign(2*n, elem_ident);
        lazy_operands.assign(2*n, lazy_operand_ident);
    }

    void build(const vector<Elem>& v){
        int n_temp = v.size();
        init(n_temp);
        rep(i,n_temp) elems[n+i] = v[i];
        for (int i=n-1; i>0; --i) {
            elems[i] = (*f)(elems[i*2], elems[i*2+1]);
        }
    }

    inline void assign_merged_lazy(LazyOperand& dest, LazyOperand x) {
        dest = (*h)(dest, x);
    }

    inline Elem reflect(int k){
        return (lazy_operands[k] == lazy_operand_ident) ? elems[k] : (*g)(elems[k], lazy_operands[k]);
    }

    inline void _eval(int k){
        if (lazy_operands[k] != lazy_operand_ident) {
            assign_merged_lazy(lazy_operands[k*2], lazy_operands[k]);
            assign_merged_lazy(lazy_operands[k*2+1], lazy_operands[k]);

            elems[k] = reflect(k);
            lazy_operands[k] = lazy_operand_ident;
        }
    }

    inline void eval_down(int k) {
        for (int i=height; i>0; --i) {
            _eval(k >> i);
        }
    }

    inline void recalc(int k) {
        while (k >>= 1) {
            elems[k] = (*f)(reflect(k*2), reflect(k*2+1));
        }
    }

    void update(int a, int b, LazyOperand x) {
        a += n; b += n;
        eval_down(a);
        eval_down(b-1);
        for (int l=a,r=b; l<r; l>>=1,r>>=1) {
            if (l & 1) assign_merged_lazy(lazy_operands[l++], x);
            if (r & 1) assign_merged_lazy(lazy_operands[--r], x);
        }
        recalc(a);
        recalc(b-1);
    }

    void set_val(int a, Elem e) {
        a += n;
        eval_down(a);
        elems[a] = e;
        lazy_operands[a] = lazy_operand_ident;
        recalc(a);
    }

    Elem query(int a, int b) {
        a += n; b += n;
        eval_down(a);
        eval_down(b-1);
        Elem vl = elem_ident, vr = elem_ident;
        for (int l=a,r=b; l<r; l>>=1,r>>=1) {
            if (l & 1) vl = (*f)(vl, reflect(l++));
            if (r & 1) vr = (*f)(reflect(--r), vr);
        }
        Elem merged = (*f)(vl, vr);
        return merged;
    }

    void desc() {
    }
};


template <typename T, int base=0>
class fenwick_tree_0 {
 public:
    vector<T> x;
 public:
    fenwick_tree_0(int n) : x(n+base,0) { }
    void add(int k, T a) { for (; k<x.size(); k|=k+1) x[k] += a; }
    T sum(int i, int j) {
        if (i == base) {
            T S = 0; for (; j>=0; j=(j&(j+1))-1) S += x[j]; return S;
        } else {
            return sum(base, j) - sum(base, i-1);
        }
    }
};

template <typename T, int base=1>
class fenwick_tree_1 {
 public:
    vector<T> x;
 public:
    fenwick_tree_1(int n) : x(n+base,0) { }
    void add(int k, T a) { for (; k<=x.size(); k+=k&-k) x[k] += a; }
    T sum(int i, int j) {
        if (i == base) {
            T S = 0; for (; j>0; j-=j&-j) S += x[j]; return S;
        } else {
            return sum(base, j) - sum(base, i-1);
        }
    }
};

template <typename F, typename T, int base>
class double_fenwick_tree {
public:
    F p, q;
public:
    double_fenwick_tree(int n) : p(n), q(n) { }

    void add_range(int a, int b, T w) {
        p.add(a, -w*a); p.add(b, w*b);
        q.add(a, w); q.add(b, -w);
    }
#if 0
    T sum(int i, int j) {
        if (i == base) {
            return p.sum(base, j) + j*q.sum(base, j);
        } else {
            return sum(base, j+1) - sum(base, i);
        }
    }
#else
    T sum(int i, int j) {
        if (i == base) {
            return p.sum(base, j) + j*q.sum(base, j);
        } else {
            return sum(base, j) - sum(base, i);
        }
    }
#endif
};



ll solve(int N, int D, int A, vi& x, vi& h) {
    auto consume = [&](int x){
        return (x + A-1) / A;
    };
    using P=pair<ll,ll>;
    vector<P> xh(N);
    rep(i,N) {
        xh[i] = P(x[i], consume(h[i]));
    }
    sort(ALL(xh));

    double_fenwick_tree<fenwick_tree_0<ll>, ll, 0> ft(N+1);

    ll w = D*2;
    ll eaten = 0;

    for (int i=0; i<N; ++i){
        ll ate = ft.sum(i, i+1);
        ll till = xh[i].second - ate;
        if (till <= 0) continue;

        ll x = xh[i].first;
        int j = upper_bound(ALL(xh), P(x+w, INT_MAX)) - xh.begin();
        ft.add_range(i, j, till);
        eaten += till;
    }

    return eaten;
}

int main(){

    int N, D, A;
    scanf("%d %d %d%*c", &N, &D, &A);
    vi x(N), h(N);
    rep(i,N){
        scanf("%d %d%*c", &x[i], &h[i]);
    }
    cout << solve(N,D,A,x,h) << endl;
    return 0;
}


Measured memory_bytes: 8064