memory007

#include <fstream>
#include <bitset>
using namespace std;
ifstream f("memory007.in");
ofstream g("memory007.out");
bitset<700001>v;

int main()
{
    long n,m,a,b,i,j,nr,x;
    long long s;
    f>>n>>m>>a>>b;
    for(i=1;i<=n;++i)
    {
        f>>x;
        j=x-a;
        v[j]=1;
    }
    j=0;
    nr=0;
    s=0;
    for(i=1;i<=m;++i)
    {
        f>>x ;
        while(nr<x)
          nr+=v[j],++j;
        s+=j-1;
    }
    s=s+(long long)m*a;
    g<<s;
    return 0;
}