import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container, std.format;
static import std.ascii;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long N, D, A;
    scan(N, D, A);
    auto X = new long[](N);
    auto H = new long[](N);
    foreach (i; 0 .. N)
        scan(X[i], H[i]);
    zip(X, H).sort();
    long R = 2 * D + 1;
    auto imos = new long[](N + 1);
    long j;
    long ans;
    foreach (i; 0 .. N)
    {
        imos[i] += imos[max(i - 1, 0)];
        // writefln("%s %s %s", i, H[i], imos);
        if (0 < H[i] - imos[i])
        {
            // writefln("%s %s", i, H[i] - imos[i]);
            long remain = H[i] - imos[i];
            long cnt = (remain + A - 1) / A;
            long damage = cnt * A;
            while (j <= N && X[j] < X[i] + R)
                j++;
            imos[i] += damage;
            imos[j] -= damage;
            ans += cnt;
        }
    }
    writeln(ans);
}
