#include "bits/stdc++.h"
using namespace std;

#define DEBUG(x) cout<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
const int inf = 1000000001;
const ll INF = 2e18 * 2;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };


int main() {
	int n, k, i, j;
	cin >> n >> k;
	vl w(n), d(n);
	for (i = 0; i < n; i++) {
		cin >> w[i] >> d[i];
	}
	ll left = 0, right = INF;
	while (left + 1 < right) {
		ll mid = (left + right) / 2;
		ll cnt = 0;
		for (i = 0; i < n; i++) {
			if (mid < w[i]) {
				continue;
			}
			cnt += (mid - w[i] + d[i]) / d[i];
			if (cnt < 0) {
				cnt = INF;
				break;
			}
		}
		if (cnt >= k) {
			right = mid;
		}
		else {
			left = mid;
		}
	}
	cout << right << endl;
}