#include <bits/stdc++.h>

using namespace std;
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define rrep(i,n) for(int i=n-1;i>=0;--i)
#define debug(output) if(debugFlag)cout<<#output<<"= "<<output<<"\n";
using lint = long long;
typedef pair<int,int> P;
const bool debugFlag=true;
const lint linf=1.1e18;const int inf=1.01e9;
constexpr int MOD=1000000007;
template<class T>bool chmax(T &a, const T &b) { if(a <= b){ a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if(a > b){ a = b; return 1; } return 0; }

void solve(vector<int>& a,vector<int>& b,int k){
    int n=a.size();int m=b.size();
    map<int,multiset<int>> mp;
    rep(i,m)mp[b[i]%k].insert(b[i]);
    lint res=0;
    sort(a.begin(),a.end());
    rep(i,n){
        auto& v=mp[a[i]%k];
        auto it=v.lower_bound(a[i]);
        int mn=inf;
        if(it!=v.end())chmin(mn,(*it-a[i])/k);
        if(it!=v.begin()){
            --it;
            if(chmin(mn,(a[i]-*(it))/k))v.erase(it);
            else{
                ++it;
                if(it!=v.end())v.erase(it);
            }
        }
        res+=mn;
    }
    if(res>=inf)res=-1;
    cout<<res<<"\n";
}

signed main(){
    int n,m,k;cin>>n>>m>>k;
    vector<int> a(n),b(m);
    rep(i,n)cin>>a[i];
    rep(i,m)cin>>b[i];
    if(n>m)swap(a,b);
    solve(a,b,k);
    return 0;
}