#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define fi first
#define se second
int n;
ll c;
set<pair<ll,int> >s,ps;
set<pair<ll,int> >dl;
ll dy=0;
ll t[200001],d[200001];
int main(){
	ios::sync_with_stdio(false);cin.tie(0);
	cin >> n >> c;
	ll ans=0;
	ll ct=0;
	for(int i=1; i<=n ;i++){
		cin >> t[i] >> d[i];
		t[i]=t[i]-d[i]+1;
		s.insert({d[i],i});
		ans+=t[i];
	}
	if(ans<=c){
		cout << "0\n";
		return 0;
	}
	while(s.size()>c){
		ps.insert(*s.begin());
		s.erase(s.begin());
	}
	for(auto c:s){
		int x=c.se;
		dy+=d[x];
		dl.insert({ct+t[x]/d[x],x});
	}
	while(true){
		ll nt=dl.begin()->fi;
		if(ans-(nt-ct)*dy<=c){
			ll res=ct+(ans-c+dy-1)/dy;
			cout << res << '\n';
			return 0;
		}
		ans-=(nt-ct)*dy;
		ct=nt;
		int x=dl.begin()->se;
		dl.erase(dl.begin());
		if(x<=n){
			dy-=d[x];
			s.erase({d[x],x});
			ps.insert({t[x]%d[x],x+n});
		}
		else{
			x-=n;
			s.erase({t[x]%d[x],x+n});
			dy-=t[x]%d[x];
		}
		if(!ps.empty()){
			auto it=ps.end();--it;
			int x=it->se;ps.erase(it);
			if(x<=n){
				s.insert({d[x],x});
				dl.insert({ct+t[x]/d[x],x});
				dy+=d[x];
			}
			else{
				x-=n;
				s.insert({t[x]%d[x],x+n});
				dl.insert({ct+1,x+n});
				dy+=t[x]%d[x];
			}
		}
	}
}