//Nguyen Huu Hoang Minh
#include <bits/stdc++.h>
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define reset(x) memset(x, 0,sizeof(x))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define N 100005
#define remain(x) if (x > MOD) x -= MOD
#define ii pair<int, int>
#define iiii pair< ii , ii >
#define viiii vector< iiii >
#define vi vector<int>
#define vii vector< ii >
#define bit(x, i) (((x) >> (i)) & 1)
#define Task "test"
#define int long long

using namespace std;

typedef long double ld;
const int inf = 1e10;
const int minf = -1e10;

int n, m;
int a[N], b[N];

void readfile()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    if (fopen(Task".inp","r"))
    {
        freopen(Task".inp","r",stdin);
        //freopen(Task".out","w",stdout);
    }
    cin >> n >> m;
    for(int i=1; i<=n; i++){
        cin >> a[i] >> b[i];
    }
}

bool ok(int day){
    int product = 0;
    for(int i=1; i<=n; i++){
        int bi =  b[i]+1;
        int full = day/bi;
        int lef = day%bi;
        product += full*b[i]*a[i] + lef*a[i];
    }
    return product >= m;
}

void proc()
{
    int l = 1, r = 1e18;
    while (r-l>0){
        int mid = (l+r)/2;
        if (ok(mid)) r = mid;
        else l = mid+1;
    }
    cout << l;
}

signed main()
{
    readfile();
    proc();
    return 0;
}