//#pragma GCC optimize("O3,unroll-loops,Ofast")
//#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define MAX 200007
#define pb push_back
#define mp make_pair
#define int long long
#define f first
#define s second
#define vi vector<int>
#define pii pair<int,int>
#define si set<int>
#define vpii vector<pair<int,int>>
const int mod = 1e9+7;
const int INF = 1e18;
// myMap.begin()->first : key
// myMap.begin()->second : value
int epow(int a,int b){int ans=1;while(b){if(b&1) ans*=a;a*=a;;b>>=1;}return ans;}
int gcd(int a,int b) {if(a<b)swap(a,b);while(b){int tmp=b;b=a%b;a=tmp;}return a;}
int mul(int a,int b){return ((a%mod)*(b%mod))%mod;}
int sum(int a,int b){return ((a%mod)+(b%mod))%mod;}
//typedef tree<pii,null_type,less<pii>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
void solve(){
int m,d,n; cin>>m>>d>>n;
vi v(n); for(int i=0;i<n;i++) cin>>v[i];
sort(v.begin(),v.end(),greater<int>());
int curr=0,sayi=0;
for(int i=0;i<n;i++){
if(curr<d){
if(v[i]<=d-curr) break;
v[i]-=d-curr;
curr+=v[i];
sayi++;
if(curr>=m) break;
}
else{
curr=max(curr,v[i]+d);
sayi++;
if(curr>=m) break;
}
}
if(curr>=m) cout<<sayi<<endl;
else cout<<"0"<<endl;
return;
}
int32_t main() {
// freopen("hayfeast.in", "r", stdin);
// freopen("hayfeast.out", "w", stdout);
ios_base::sync_with_stdio(0);cin.tie(0);
int t=1;
// cin >> t;
while (t--) solve();
return 0;
}
