#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define mp make_pair
#define ll long long
using namespace std;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ll n, c;
    cin >> n >> c;
    vector<pair<ll, ll>> v(n);
    ll total = 0;
    for(ll i = 0; i < n; ++i)
        cin >> v[i].fi >> v[i].se, total += v[i].fi;
    ll l = 1, r = 1e18 + 5, ans = -1;
    while(l <= r) {
        ll mid = (l + r) / 2;
        // cerr << mid << endl;
        vector<pair<ll, pair<ll, ll>>> red;
        for(auto p : v) {
            if(ceil(p.fi / (double)p.se) <= mid) {
                red.pb(mp(p.se, mp(p.fi / p.se, 0)));
                if(p.fi % p.se != 0) {
                    if(ceil(p.fi / (double)p.se) == mid) {
                        red.pb(mp(p.fi % p.se, mp(1, 1)));
                    }
                    else {
                        red.pb(mp(p.fi % p.se, mp(1, 0)));
                    }
                }
            }
            else {
                red.pb(mp(p.se, mp(mid, 0)));
            }
        }
        sort(red.begin(), red.end());
        ll lst = 0;
        ll rem = 1ll * c * mid;
        ll cur = total;
        while(red.size() && rem > 0) {
            ll init = rem;
            cur -= red.back().fi * min((ll)red.back().se.fi, rem);
            rem -= min((ll)red.back().se.fi, rem);
            red.pop_back();
            if(init - rem == mid || red.back().se.se)
                ++lst;
        }
        ll rem_time = min((ll)c - lst, rem);
        if(cur - rem_time <= 0) {
            ans = mid, r = mid - 1;
        }
        else
            l = mid + 1;
    }
    cout << ans - 1 << endl;
    return 0;
}