#include <bits/stdc++.h>
#define pii pair<int,int>
#define F first
#define S second
#define mp make_pair
using namespace std;
const int inf=1e9;
int main(){
int n,m,k;
cin>>n>>m>>k;
vector<int> a(n);
for(int&x:a) cin>>x;
vector<int> c(m);
for(int&x:c) cin>>x;
int s=0;
for(int&x:a){
s+=x;
if(k>x){
cout<<"Impossible";
return 0;
}
}
vector<vector<int>> mem(m+1,vector<int>(300*300+1,-1));
function<int(int,int)> dp=[&](int index,int sum){
if(index==m&&sum==0) return 0;
if(index==m) return -inf;
if(mem[index][sum]!=-1) return mem[index][sum];
return mem[index][sum]=max(dp(index+1,sum),(sum>=c[index]?dp(index+1,sum-c[index])+min(c[index],n):-inf));
};
for(int i=s;i<=300*300;i++)
if(dp(0,i)>=k*n){
cout<<i-s;
return 0;
}
cout<<"Impossible";
return 0;
}
