#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;


bool check(int n, LL m, int c, const vector<PII>& a)
{
	multiset<PII> cands;
	
	FOR(i, 0, n)
	{
		cands.insert(MP(-a[i].S, a[i].F));
	}
	
	
	LL time = 0;
	while(SZ(cands))
	{
		auto [d, t] = *cands.begin();
		cands.erase(cands.begin());
	
		d = -d;
		
		int cnt = t / d;
		
		if(m >= cnt)
		{
			time += cnt;
			if(t % d != 0)
			cands.insert(MP(-(t % d), t % d));
		}
		else
		{
			time += m;
			time += t - m * d;
		}
	}
	
	return time <= (__int128)c * m;
}


int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int n, c;
	cin >> n >> c;
	vector<PII> a(n);
	FOR(i, 0, n)
		cin >> a[i].F >> a[i].S;
	
	LL l = 0, r = (LL)n * c;
	
	while(r - l > 1)
	{
		LL m = (l + r) / 2;
		if(check(n, m, c, a))
			r = m;
		else
			l = m;
	}
	cout << r << "\n";
	
	return 0;
}