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;
    long ans;
    foreach (i; 0 .. N)
        if (0 < H[i])
        {
            long cnt = (H[i] + A - 1) / A;
            ans += cnt;
            inner: foreach (j; i + 1 .. N)
                if (X[j] < X[i] + R)
                {
                    H[j] -= cnt * A;
                }
                else
                {
                    break inner;
                }
        }
    writeln(ans);
}
