#include<iostream>
#include<cstdio>
#include<cmath>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<algorithm>
#include<functional>
#include<cstring>
#include<deque>
using namespace std;
int main()
{
    long long N,D,R,ans;
    int Day[100],Night[100];
    while(cin>>N>>D>>R)
    {
        if(N==0)break;
        for(int i=0;i<N;++i)cin>>Day[i];
        for(int i=0;i<N;++i)cin>>Night[i];
        sort(Day,Day+N);
        sort(Night,Night+N,greater<int>());
        ans=0;
        for(int i=0;i<N;++i)
        {
            int all=Day[i]+Night[i];
            if(all>D)ans+=R*(all-D);
        }
        cout<<ans<<endl;
    }
}

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MiAyMCA1CjEwIDE1CjEwIDE1CjIgMjAgNQoxMCAxMAoxMCAxMCAKMCAwIDAg

2 20 5
10 15
10 15
2 20 5
10 10
10 10 
0 0 0