#include <bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pl3 tuple<ll, ll, ll>
#define pdd pair<double, double>
#define F first
#define S second
#define all(x) x.begin(), x.end()

using namespace std;

ll N, C, D[200005], T[200005];
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    cin >> N >> C;
    for (int i = 1; i <= N; i++)
        cin >> T[i] >> D[i];
    // k days: k - 1 free days + 1 complete day
    auto check = [&](ll k)
    {
        ll remain = k * C, over = 0, total = 0;
        priority_queue<pl3> pq;
        for (int i = 1; i <= N; i++)
            pq.push(make_tuple(D[i], T[i], k));
        while (!pq.empty())
        {
            auto [d, t, u] = pq.top();
            pq.pop();
            ll use = min({u, remain, t / d});
            u -= use, remain -= use, t -= use * d; 
            if (u == 0)
                over++, total += t;
            else if (remain == 0)
                total += t;
            else if (t > 0) // arrive at last remainder
                pq.push(make_tuple(min(d, t), t, u));
        }
        total += max(over, C - remain);
        return total <= C;
    };
    ll l = 1, r = (N * 2e9) / C;
    while (l < r)
    {
        ll mid = (l + r) / 2;
        if (check(mid))
            r = mid;
        else
            l = mid + 1;
    }
    cout << l - 1 << '\n';
}