#include<bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp> //required
#include <ext/pb_ds/tree_policy.hpp> //required

using namespace __gnu_pbds; 
using namespace std;

template <typename T> using ordered_set =  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; 
// find_by_order(k)  returns iterator to kth element starting from 0;
// order_of_key(k) returns count of elements strictly smaller than k;
typedef long long  ll;
typedef vector<ll> VL;
typedef vector<int> VI;
typedef pair<ll,ll> PLL;
typedef pair<int,int> PII;
#define pb push_back

#define F first
#define S second
#define SZ(a) int((a).size())
#define ALL(a) a.begin(),a.end()
#define fr(i,x,y) for(int i=x;i<y;i++)
#define frr(i,x,y) for(int i=x-1;i>=y;i--)
#define inf 1e18+1
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
const int mod=1000000007;
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
ll power(ll a,ll b){ll ans=1;while(b!=0){if(b&1){ans*=a;}a=a*a;b>>=1;}return ans;}
ll powerm(ll a,ll b){ll ans=1;while(b!=0){if(b&1){ans*=a;ans%=mod;}a=a*a;a%=mod;b>>=1;}return ans%mod;}
// string to integer stoi()
// string to long long stoll()
// string.substr(position,length);
// integer to string to_string();

void solve()
{
    ll n,x;
    cin>>n>>x;
    ll ct=0;
    VL arr(n);
    fr(i,0,n)
        cin>>arr[i];
    fr(i,1,n)
    {
        if((arr[i]+arr[i-1])>x)
        {
            ll rem=(arr[i]+arr[i-1])-x;
            ll f=min(rem,arr[i]);
            rem-=f;
            arr[i]-=f;
            ct+=f;
            if((arr[i]+arr[i-1])>x)
            {
                ct+=rem;
            }
        }
    }
    cout<<ct<<endl;
    return;
}
int main()
{
    IOS;
    ll t=1;
    //cin>>t;
    while(t--)
    {
        //cout<<"Case #"<<pp-t<<":\n";
        solve();
    }
    return 0;
}
/* stuff you should look for
        * int overflow, array bounds
        * special cases (n=1?)
        * do smth instead of nothing and stay organized
        * WRITE STUFF DOWN
*/
/*
recursion - matrix exponential

*/
// BITMASK:
// 1)When some constrall is of the order of 15-20, think of bitmask DP.
// 2)When some constrall is around 40, try out meet in the middle
// 3) See Strings,palindromes,prefix,suffix etc -> KMP,Z algorithm
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<cmath>
#include<cstdio>
#include<queue>
#include<deque>
#include<map>
#include<stack>
#include<set>
#include<utility>
using namespace std;
typedef pair<int,int> ii;
typedef long long ll;
typedef pair<ll,ll> p;
typedef unsigned long long int ull;
const ll MOD=998244353;
int dy[]={1,0,-1,0};
int dx[]={0,1,0,-1};
const int MAXN=100000;
const int MAXE=100000;
const int MAXV=10000;
const ll INF=2e9;

ll N,M,V,P;
ll A[100000];

bool C(int x){
    if(x<P) return true;
    if(A[x]+M<A[P-1]) return false;
    ll sum=0;
    sum+=M*P;
    sum+=M*(N-1-x);
    for(int i=P-1;i<x;i++){
        sum+=min(M,A[x]+M-A[i]);
    }
    return sum>=M*V;
}

int main(){
    cin>>N>>M>>V>>P;
    for(int i=0;i<N;i++) cin>>A[i];
    sort(A,A+N,greater<ll>());
    int l=0,r=N;
    while(r-l>1){
        int m=(l+r)/2;
        if(C(m)) l=m;
        else r=m;
    }
    cout<<l+1<<endl;
    return 0;
}