#include <bits/stdc++.h>
using namespace std;
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
#define pb push_back
#define ll long long
#define sz(s) int(s.size()
#define all(v) v.begin(),v.end()
int mod = 1e8;
const int N = 1e6;
const int inf = 2e9;
int dp[N];
signed main(){
//freopen("shuffle.in", "r", stdin);
//freopen("shuffle.out", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int n,m,k;
cin >> n >> m >> k;
int a[n + 1],b[m + 1];
for(int i = 1; i <= n; i++) cin >> a[i];
for(int i = 1; i <= m; i++) cin >> b[i];
if(m < k){
cout << "Impossible";
return 0;
}
sort(b + 1, b + 1 + m);
int ans = 1e9;
if(k != 1){
for(int mask = 0; mask < (1 << m); mask++){
vector <int> v1;
for(int i = 0; i < m; i++){
if((mask >> i & 1) == 1){
v1.pb(b[i + 1]);
}
}
if(v1.size() < k) continue;
bool f = 0;
for(int i = 1; i <= n; i++){
if(a[i] < k){
f = 1;
break;
}
int j = v1.size() - 1,cnt = k;
while(j >= 0 && cnt > 0){
cnt--;
if(v1[j] <= 0){
f = 1;
break;
}
v1[j]--;
j--;
}
if(f == 1) break;
sort(v1.begin(),v1.end());
}
if(f == 0){
int sum = 0,sum1 = 0;
for(int i = 1; i <= n; i++) sum += a[i];
for(int i = 0; i < v1.size(); i++) sum1 += v1[i];
sum -= (k * n);
if(sum <= sum1){
ans = min(ans,sum1 - sum);
}
}
}
if(ans == 1e9) cout << "Impossible";
else cout << ans;
}
else{
int w = 300 * 300;
dp[0] = 1;
int sum = 0;
for(int i = 1; i <= n; i++){
sum += a[i];
if(a[i] == 0){
cout << "Impossible";
return 0;
}
}
for(int i = 1; i <= m; i++){
for(int j = w; j >= b[i]; j--){
dp[j] = dp[j - b[i]];
}
}
for(int i = 0; i <= w; i++){
if(dp[i] == 1 && i >= sum){
ans = i - sum;
break;
}
}
if(ans == 1e9) cout << "Impossible";
else cout << ans;
}
}
