import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, std.bitmanip;

immutable long MOD = 10^^9 + 7;

void main() {
    auto s = readln.split;
    auto N = s[0].to!int;
    auto L = s[1].to!long;
    auto A = s[2].to!long;
    long[] T, X;
    foreach (i; 0..N) {
        s = readln.split;
        T ~= s[0].to!long;
        X ~= s[1].to!long;
    }
    T ~= L;
    X ~= 0;

    long t = 0;
    long ans = 0;

    foreach (i; 0..N+1) {
        long interaval = T[i] - t;
        ans += interaval / A;
        t = T[i] + X[i];
    }

    ans.writeln;
}
