#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define siz(x) (int)(x.size())
#define all(x) x.begin(), x.end()
#define debug_arr(x,len) for(int _=1; _<=len; _++) cout<<x[_]<<" "; cout<<'\n';
#define debug(x) cout<<'\n'<<#x<<": "<<x<<'\n';
const int maxN = 1e5+5;
int n, m, p, a[maxN], b[maxN];
void solve()
{
}
int32_t main()
{
freopen("CHECKIN.INP", "r", stdin);
freopen("CHECKIN.OUT", "w", stdout);
ios_base::sync_with_stdio(0); cin.tie(0);
cin>>n>>m>>p;
for(int i=1; i<=n; i+=1) cin>>a[i]>>b[i];
int l = 0, r = 9e18, ans = 0;
while(r - l >= 0)
{
int mid = (l+r)>>1;
vector<int>v;
for(int i=1; i<=n; i+=1) v.push_back(max(0ll, (mid - b[i]) / a[i]));
sort(all(v), greater<int>());
int tmp = 0, ok = 0;
for(int i=0; i<min(n,m); i+=1) tmp += v[i];
if(tmp >= p) ok = 1;
if(ok) r = mid-1, ans = mid;
else l = mid+1;
}
cout<<ans<<'\n';
}
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