// 
#include<bits/stdc++.h>
#define int long long
using namespace std;
int L,R,n,k,a[300003],dis[100003][21],dp[(1<<20)][21],lft,rgt,mid,wz,k1,k2,k3,k4,k5,ans;
double tim;
int sqz(int X,int Y){
    if(X%Y!=0)return (X/Y)+1;
    return (X/Y);
}
signed main(){
    ios::sync_with_stdio(false);
    cin>>L>>R>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    sort(a+1,a+n+1);
    for(int i=n+1;i<=3*n;i++)a[i]=a[i-n]+L;
    for(int i=0;i<=n;i++){
        for(int j=0;j<=R;j++){
            if(k!=1)wz=a[i]+j*(L/R)+min(sqz((R-j)*(L/R),k+1),sqz(j*(L/R),k-1));
            else wz=a[i]+j*(L/R)+sqz((R-j)*(L/R),k+1);
            lft=1;
            rgt=3*n;
            while(lft<rgt){
                mid=((lft+rgt)>>1);
                if(a[mid]>=wz)rgt=mid;
                else lft=mid+1;
            }
            dis[i][j]=k*(a[lft]-(a[i]+j*(L/R)));
        }
    }
    memset(dp,-1,sizeof(dp));
    dp[1][1]=0;
    for(int i=1;i<(1<<R)-1;i+=2){
        for(int j=1;j<=R;j++){
            if((i&(1<<j-1))==0)continue;
            if(dp[i][j]==-1)continue;
            wz=(L/R)*(j-1)+dp[i][j]/k;
            while(wz>=L)wz-=L;
            lft=1;
            rgt=n+1;
            while(lft<rgt){
                mid=((lft+rgt)>>1);
                if(a[mid]>=wz)rgt=mid;
                else lft=mid+1;
            }
            wz=lft;
            if(wz>n)wz-=n;
            if(i==1&&j==1)wz=0;
            for(int u=1;u<=R;u++){
                if((i&(1<<(u-1)))!=0)continue;
                if(u>j)k1=u-j;
                else k1=(u+R-j);
                if(dp[i+(1<<(u-1))][u]==-1||dp[i+(1<<(u-1))][u]>dp[i][j]+dis[wz][k1])dp[i+(1<<(u-1))][u]=dp[i][j]+dis[wz][k1];
            }
        }
    }
    ans=dp[(1<<R)-1][1];
    for(int i=2;i<=R;i++){
        if(dp[(1<<R)-1][i]==-1)continue;
        if(ans==-1||dp[(1<<R)-1][i]<ans)ans=dp[(1<<R)-1][i];
    }
    cout<<ans;
    return 0;
}