#include<bits/stdc++.h>
#define int long long
using namespace std;
signed main(){
    int n,m,x,y;
    cin>>n>>m>>x>>y;
    vector<int> a(m+2);
    a[0] = 0;
    a.back() = n+1;
    for(int i=1;i<=m;i++)cin>>a[i];
    int last = 0;
    int ad = 0;
    for(int i=1;i<a.size();i++){
        // cerr<<i<<endl;
        int d = a[i]-a[i-1]-1;
        // cerr<<d<<endl;
        if(d>y+2){
            ad += d/(y+2)*2;
            d%=y+2;
            last = max(y-x,last);
        }
        // cerr<<' '<<d<<endl;
        while(1){
            int d1 = x;
            int d2 = y-last;
            int dd = min(d1,d2);
            if(dd>=d){
                last = d;
                break;
            }
            last = dd;
            d-=dd+1;
            ad++;
        }
    }
    cout<<ad<<endl;


}