#include<bits/stdc++.h>
using namespace std;
#define FOR(i,s,t) for(int i=(s),_t=(t); i<=_t; ++i)
#define DOR(i,s,t) for(int i=(s),_t=(t); i>=_t; --i)t
typedef double db;
const int N=2005;
db a[N],s[N],s2[N];
db f[N][105];
int main() {
    int m,n,K,d;
    scanf("%d%d%d%d",&m,&n,&K,&d);
    // db res=m*d*d-1.0*m*d*m*d/(m+n);
    db res=1.0*(m+n)*d*d/4;
    // cerr << res << endl;
    n+=m;
    FOR(i,1,n) scanf("%lf",&a[i]);
    sort(a+1,a+n+1);
    FOR(i,1,n) {
        s[i]=s[i-1]+a[i];
        s2[i]=s2[i-1]+a[i]*a[i];
    }
    FOR(i,1,n) {
        f[i][0]=1e18;
        FOR(k,1,K) {
            f[i][k]=1e18;
            FOR(j,0,i-1) {
                f[i][k]=min(f[i][k],f[j][k-1]+s2[i]-s2[j]-(s[i]-s[j])*(s[i]-s[j])/(i-j));
            }
        }
    }
    printf("%.9lf\n",f[n][K]+res);
    return 0;
}