#include <bits/stdc++.h>
using namespace std;
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define _repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define _rep(i,n) _repl(i,0,n)
#define rep(...) GET_MACRO(__VA_ARGS__, _repl, _rep)(__VA_ARGS__)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back((a))
#define all(x) (x).begin(),(x).end()
#define uniq(x) sort(all(x)),(x).erase(unique(all(x)),end(x))
#define fi first
#define se second
#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
void _dbg(string){cout<<endl;}
template<class H,class... T> void _dbg(string s,H h,T... t){int l=s.find(',');cout<<s.substr(0,l)<<" = "<<h<<", ";_dbg(s.substr(l+1),t...);}
template<class T,class U> ostream& operator<<(ostream &o, const pair<T,U> &p){o<<"("<<p.fi<<","<<p.se<<")";return o;}
template<class T> ostream& operator<<(ostream &o, const vector<T> &v){o<<"[";for(T t:v){o<<t<<",";}o<<"]";return o;}

#define INF 1120000000
#define long long long // for codeforces

int main(){
  int n; long k;
  cin>>n>>k;

  vector<long> w(n), d(n);
  rep(i,n) cin>>w[i]>>d[i];

  long l = 0, r = LLONG_MAX/3;
  // l の位置はk未満, rがk以上
  while(r-l>1){
    long m = (r-l)/2+l;
    long cnt = 0;
    rep(i,n) if(w[i]<=m){
      cnt += (m-w[i]+d[i])/d[i];
    }
    // dbg(l,r,m,cnt);
    if(cnt >= k) r = m;
    else l = m;
  }

  cout << r << endl;

  return 0;
}
