FORESTGA

#include <iostream>
using namespace std;
typedef long long ll;
typedef long double ld;
#include<bits/stdc++.h>
#include "limits.h"
typedef priority_queue<ll> pq;
#define pb push_back
#define mp make_pair
#define find_max *max_element
#define mod 1

ll N,W,L;

ll cal_wood(ll t,ll H[],ll R[]){
    ll woods=0;
    for(ll i=0;i<N;++i){
        ll temp=H[i]+(R[i]*t);
        if(temp>=L)woods+=temp;
        if(woods>=W)return woods;
    }
    return woods;
}





int main() {
    
	cin>>N>>W>>L;
	ll H[N],R[N];
	for(ll i=0;i<N;++i)cin>>H[i]>>R[i];

	ll temp=cal_wood(0,H,R);
	if(temp>=W)cout<<"0\n";
	else{
	    
	    ll i=1,j=1e+18;
        ll month=-1;
        
        while(i<=j){
            ll mid=(i+j)/2;
            ll temp=cal_wood(mid,H,R);
            if(temp>=W){
                month=mid;
                j=mid-1;
            }else i=mid+1;
            
        }
	    cout<<month<<"\n";
	}   
	
}