#include <bits/stdc++.h>
int n, p, m;
int d[100010], t[100010];
int main() {
  scanf("%d%d%d", &n, &p, &m);
  d[0] = 1;
  d[n + 1] = m + 1;
  for (long long i = (long long)(1); i < (long long)(n + 1); i++) {
    scanf("%d%d", d + i, t + i);
  }
  long long res = 0;
  long long crt = 0;
  for (long long i = (long long)(0); i < (long long)(n + 1); i++) {
    long long dd = d[i + 1] - d[i];
    long long lb = -1, ub = m * 2;
    while (ub - lb > 1) {
      long long mid = (lb + ub) / 2;
      if (crt - mid * p < 0)
        ub = mid;
      else
        lb = mid;
    }
    long long j = ub - 1;
    j = (0LL > j ? 0LL : j);
    res += (0LL > dd - j ? 0LL : dd - j);
    crt += -p * dd + t[i + 1];
  }
  printf("%lld\n", res);
  return 0;
}
