#include <bits/stdc++.h>
using namespace std;
const int INF = 2034567891;
const long long int INF64 = 4234567890123456789ll;
long long nc3(long long v) { return (v * (v - 1ll) * (v - 2ll)) / 6ll; }
long long nc2(long long v) { return (v * (v - 1ll)) / 2ll; }
long long int gcd(long long int a, long long int b) {
  return (b == 0 ? a : gcd(b, a % b));
}
long long int lcm(long long int a, long long int b) {
  return (a * (b / gcd(a, b)));
}
const int N = 10 + 2e5;
bool isprime(long long int n) {
  if (n < 2) return 0;
  if (n == 2) return 1;
  if (n % 2 == 0) return 0;
  for (long long int i = 3; i * i <= n; i++)
    if (n % i == 0) return 0;
  return 1;
}
double dist(pair<long long int, long long int> p1,
            pair<long long int, long long int> p2) {
  return (p1.first - p2.first) * (p1.first - p2.first) +
         (p1.second - p2.second) * (p1.second - p2.second);
}
long long int power(long long int x, long long int y) {
  long long int ans = 1;
  while (y > 0) {
    if (y & 1) ans = (ans * x) % 1000000007;
    x = (x * x) % 1000000007;
    y /= 2;
  }
  return ans % 1000000007;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int n, m, a, b;
  cin >> n >> m;
  long long int sum = 0;
  vector<long long int> v;
  for (long long int i = 0; i < n; i++) {
    cin >> a >> b;
    sum += a;
    v.push_back(a - b);
  }
  sort(v.begin(), v.end());
  long long int cnt = 0;
  while (v.size() && sum > m) {
    sum -= v.back();
    v.pop_back();
    cnt++;
  }
  if (sum <= m)
    cout << cnt;
  else
    cout << "-1";
}
