#define _CRT_SECURE_NO_WARNINGS

#include <bits/stdc++.h>

//#define FAST_ALLOCATOR_MEMORY 2e8
//#include "optimization.h"

using namespace std;

#define ALL(x) x.begin(), x.end()

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int,int> pii;

const int inf = (int)1e9;
const ll md = (ll)1e9 + 7, inf64 = (ll)1e18;

int main() {
    iostream::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

#ifdef LOCAL
    freopen("C:\\Users\\aytel\\CLionProjects\\common\\input.txt", "r", stdin);
    freopen("C:\\Users\\aytel\\CLionProjects\\common\\output.txt", "w", stdout);
#endif

    int n, m;
    cin >> n >> m;

    ll sum = 0;
    vector<ll> diff;
    for (int i = 0; i < n; i++) {
        ll a, b;
        cin >> a >> b;
        sum += a;
        diff.push_back(a - b);
    }
    sort(diff.begin(), diff.end());
    while (diff.size() && sum > m) {
        sum -= diff.back();
        diff.pop_back();
    }

    if (sum > m)
        cout << -1;
    else
        cout << n - (diff.size()) << '\n';

    return 0;
}