#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#ifdef DEBUG
template<typename T>
ostream& operator << (ostream &out,const vector<T> &x){
	out<<'[';
	for(auto y:x)out<<y<<',';
	return out<<']';
}
template<typename T>
vector<T> ary(const T *a,int l,int r){
	return vector<T>{a+l,a+1+r};
}
template<typename T>
void debug(T x){
	cerr<<x<<endl;
}
template<typename T,typename ... S>
void debug(T x,S...y){
	cerr<<x<<' ',debug(y...);
}
#else
#define debug(...) void()
#endif
const int N=2e5+10;
const ll INF=1e18;
int T,n,m,c,t[N],d[N],cur[N],a[N];
bool cmp(int x,int y){
	return d[x]>d[y];
}
bool chk(ll mid){
	copy(t,t+1+n,a);
	ll lim=mid*c;
	for(int x=1,i;i=cur[x],x<=n;x++){
		int t=min({(ll)(a[i]-1)/d[i],mid,lim});
		lim-=t,a[i]-=t*d[i];
	}
	for(int x=1,i;i=cur[x],x<=n;x++){
		if(lim&&(t[i]-1)/d[i]<mid)a[i]=0,lim--;
	}
	ll res=0;
	for(int i=1;i<=n;i++)if(a[i])res+=max(0,a[i]-d[i])+1;
	return res<=c;
}
void get(){
	scanf("%d%d",&n,&c);
	for(int i=1;i<=n;i++)scanf("%d%d",&t[i],&d[i]);
	iota(cur,cur+1+n,0),sort(cur+1,cur+1+n,cmp);
	// debug(chk(0));
	ll l=-1,r=INF/c,mid;
	for(;l+1<r;){
		mid=(l+r)>>1;
		if(chk(mid))r=mid;
		else l=mid;
	}
	printf("%lld\n",r);
}
int main(){
	for(T=1;T--;)get();
	return 0;
}