#include<bits/stdc++.h>
#define file(F) freopen(#F".in","r",stdin),freopen(#F".out","w",stdout)
#define lowbit(x) ((x)&-(x))
#define ALL(x) x.begin(),x.end()
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define popcount(x) (__builtin_popcount((x)))
using namespace std;
using ll=long long;
using uint=uint32_t;
template<typename T>
inline bool Max(T &x,T y) { return std::less<T>()(x,y)&&(x=y,true); }
template<typename T>
inline bool Min(T &x,T y) { return std::less<T>()(y,x)&&(x=y,true); }
void Solve();
const int N = 2e3+23;
int n,m,k,l;
double x[N],f[N][N],s[N],S[N];
signed main() {
#ifndef ONLINE_JUDGE
#endif
   cin.tie(nullptr)->sync_with_stdio(false);
   Solve();
}
void Solve() {
   cin>>n>>m>>k>>l; n+=m;
   for(int i=1;i<=n;i++) cin>>x[i];
   sort(x+1,x+n+1);
   for(int i=0;i<=n;i++) for(int j=0;j<=k;j++) 
      f[i][j]=1e9;
   for(int i=1;i<=n;i++) s[i]=s[i-1]+x[i],S[i]=S[i-1]+x[i]*x[i];
   f[0][0]=0;
   for(int i=1;i<=n;i++) for(int j=1;j<=k;j++)
      for(int k=0;k<i;k++) Min(f[i][j],f[k][j-1]+S[i]-S[k]-(s[i]-s[k])*(s[i]-s[k])/(i-k));
   printf("%.10lf\n",f[n][k]+n*l*l/4);
}