#include <iostream>
#include <fstream>
#include <cassert>
#include <typeinfo>
#include <vector>
#include <stack>
#include <cmath>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <cstdio>
#include <queue>
#include <iomanip>
#include <cctype>
#include <random>
#include <complex>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<30;
const ll INF=1ll<<61;
const double pi=acos(-1);
const double eps=1e-7;
const ll mod=1e9+7;
const int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};

ll n,k;
vl a,b;

bool f(ll x){
	ll t=0;
	for(int i=0;i<n;i++) if(x>=a[i]) t+=(x-a[i])/b[i]+1;
	return t>=k;
}

int main(){
	cin>>n>>k;
	a=b=vl(n);
	for(int i=0;i<n;i++) cin>>a[i]>>b[i];
	ll l=0,r=INF;
	while(r-l>1){
		ll m=(l+r)/2;
		if(f(m)) r=m;
		else l=m;
	}
	cout<<r<<endl;
}