#include <bits/stdc++.h>
#include <sys/time.h>
using namespace std;

#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define repi(i,a,b) for(long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template<class T1, class T2> bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

using ll = long long; using vll = vector<ll>; using vvll = vector<vll>; using P = pair<ll, ll>;
using ld = long double;  using vld = vector<ld>; 
using vi = vector<int>; using vvi = vector<vi>; vll conv(vi& v) { vll r(v.size()); rep(i, v.size()) r[i] = v[i]; return r; }

inline void input(int &v){ v=0;char c=0;int p=1; while(c<'0' || c>'9'){if(c=='-')p=-1;c=getchar();} while(c>='0' && c<='9'){v=(v<<3)+(v<<1)+c-'0';c=getchar();} v*=p; }
template <typename T, typename U> ostream &operator<<(ostream &o, const pair<T, U> &v) {  o << "(" << v.first << ", " << v.second << ")"; return o; }
template<size_t...> struct seq{}; template<size_t N, size_t... Is> struct gen_seq : gen_seq<N-1, N-1, Is...>{}; template<size_t... Is> struct gen_seq<0, Is...> : seq<Is...>{};
template<class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch,Tr>& os, Tuple const& t, seq<Is...>){ using s = int[]; (void)s{0, (void(os << (Is == 0? "" : ", ") << get<Is>(t)), 0)...}; }
template<class Ch, class Tr, class... Args> 
auto operator<<(basic_ostream<Ch, Tr>& os, tuple<Args...> const& t) -> basic_ostream<Ch, Tr>& { os << "("; print_tuple(os, t, gen_seq<sizeof...(Args)>()); return os << ")"; }
ostream &operator<<(ostream &o, const vvll &v) { rep(i, v.size()) { rep(j, v[i].size()) o << v[i][j] << " "; o << endl; } return o; }
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) { o << '['; rep(i, v.size()) o << v[i] << (i != v.size()-1 ? ", " : ""); o << "]";  return o; }
template <typename T> ostream &operator<<(ostream &o, const deque<T> &v) { o << '['; rep(i, v.size()) o << v[i] << (i != v.size()-1 ? ", " : ""); o << "]";  return o; }
template <typename T>  ostream &operator<<(ostream &o, const set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T>  ostream &operator<<(ostream &o, const unordered_set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U>  ostream &operator<<(ostream &o, const map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U, typename V>  ostream &operator<<(ostream &o, const unordered_map<T, U, V> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it; o << "]";  return o; }
vector<int> range(const int x, const int y) { vector<int> v(y - x + 1); iota(v.begin(), v.end(), x); return v; }
template <typename T> istream& operator>>(istream& i, vector<T>& o) { rep(j, o.size()) i >> o[j]; return i;}
template <typename T, typename S, typename U> ostream &operator<<(ostream &o, const priority_queue<T, S, U> &v) { auto tmp = v; while (tmp.size()) { auto x = tmp.top(); tmp.pop(); o << x << " ";} return o; }
template <typename T> ostream &operator<<(ostream &o, const queue<T> &v) { auto tmp = v; while (tmp.size()) { auto x = tmp.front(); tmp.pop(); o << x << " ";} return o; }
template <typename T> ostream &operator<<(ostream &o, const stack<T> &v) { auto tmp = v; while (tmp.size()) { auto x = tmp.top(); tmp.pop(); o << x << " ";} return o; }
template <typename T> unordered_map<T, ll> counter(vector<T> vec){unordered_map<T, ll> ret; for (auto&& x : vec) ret[x]++; return ret;};
string substr(string s, P x) {return s.substr(x.fi, x.se - x.fi); }
void vizGraph(vvll& g, int mode = 0, string filename = "out.png") { ofstream ofs("./out.dot"); ofs << "digraph graph_name {" << endl; set<P> memo; rep(i, g.size())  rep(j, g[i].size()) { if (mode && (memo.count(P(i, g[i][j])) || memo.count(P(g[i][j], i)))) continue; memo.insert(P(i, g[i][j])); ofs << "    " << i << " -> " << g[i][j] << (mode ? " [arrowhead = none]" : "")<< endl;  } ofs << "}" << endl; ofs.close(); system(((string)"dot -T png out.dot >" + filename).c_str()); }
size_t random_seed; namespace std { using argument_type = P; template<> struct hash<argument_type> { size_t operator()(argument_type const& x) const { size_t seed = random_seed; seed ^= hash<ll>{}(x.fi); seed ^= (hash<ll>{}(x.se) << 1); return seed; } }; }; // hash for various class
struct timeval start; double sec() { struct timeval tv; gettimeofday(&tv, NULL); return (tv.tv_sec - start.tv_sec) + (tv.tv_usec - start.tv_usec) * 1e-6; }
struct init_{init_(){ ios::sync_with_stdio(false); cin.tie(0); gettimeofday(&start, NULL); struct timeval myTime; struct tm *time_st; gettimeofday(&myTime, NULL); time_st = localtime(&myTime.tv_sec); srand(myTime.tv_usec); random_seed = RAND_MAX / 2 + rand() / 2; }} init__;
#define rand randxor
#define ldout fixed << setprecision(40) 

#define EPS (double)1e-14;
#define INF (ll)1e18;
#define mo  (ll)(1e9+7);

// 整数二分探索
// f: 単調増加関数. 000111, 111111, 000000を許容する（11110000で探索したい場合は、自分でfを反転すること）
// 閉区間[rl, rr]から単調関数fを満たす最小の数を返す。
// 全て1なら0を返す（定義通り）、全て0ならrr+1を返す（異常検出用）！
//
// xが大で1を返すような関数を作ると思うと間違えない
//
// O(log(range))
ll BinarySearch(ll rl, ll rr, function<bool(ll)> f) { 
    ll lo = rl-1, ro = rr+1;
    while (ro - lo != 1) {
        ll m = (lo + ro) / 2; 
        ((m!=rl-1&&f(m))?ro:lo)=m; 
    }
    return ro;
}
void BinarySearchInteractive(ll rl, ll rr, function<bool(ll)> f) { 
    while (1) {
        cout << "####" << endl;
        ll tmp; cin >> tmp;
        if (rl > tmp) {cout << "Out of range: too small" << endl; continue; }
        if (rr < tmp) {cout << "Out of range: too large" << endl; continue; }
        ll ret = f(tmp); cout << tmp << " : " << ret << endl;
    }
}
void BinarySearchPrint(ll rl, ll rr, function<bool(ll)> f) { 
    for (int i = rl; i <= rr; i++) cout << f(i); cout << endl;
}
void BinarySearchAssert(ll rl, ll rr, function<bool(ll)> f) { 
    bool p = false;
    for (int i = rl; i <= rr; i++) {
        bool t = f(i);
        if (p && !t) cerr << i << ": F NOT MONOTONIC INCREASE" << endl, exit(1);
        p |= t;
    }
}

// 浮動小数点二分探索
ld BinarySearchReal(ld rl, ld rr, function<bool(ld)> f) { 
    rep(i, 200) { ld m = (rl + rr) / 2; f(m)?rr=m:rl=m; }
    return rl;
}
void BinarySearchRealInteractive(ld rl, ld rr, function<bool(ld)> f) { 
    while (1) {
        cout << "####" << endl;
        ld tmp; cin >> tmp;
        if (rl > tmp) {cout << "Out of range: too small" << endl; continue; }
        if (rr < tmp) {cout << "Out of range: too large" << endl; continue; }
        ld ret = f(tmp); cout << tmp << " : " << ret << endl;
    }
}

int main(void) {
    ll n, k; cin >> n >> k;
    vll w(n), d(n);
    rep(i, n) {
        cin >> w[i] >> d[i];
    }

    auto f = [&](ll x){
        ll ret = 0;
        rep(i, n) if (w[i] <= x) {
            ret += 1 + (x - w[i]) / d[i];
        }
//        cout << ret << endl;
        return ret >= k;
    };
    rep(t, 100) {
//        cout << f(t);
    }
    cout << endl;
    ll ret = BinarySearch(0, (ll)2e18, f);
    cout << ret << endl;

    return 0;
}


Measured memory_bytes: 1788