#include <bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pb push_back
#define dd(x) cout<<#x<<" is "<<x<<endl;
#define dl(x) cout<<#x<<" is "; for(auto i:x) cout<<i<<' '; cout<<endl;
typedef pair<int,int> pii;
const int N = 305, M = 305;
int dp[M][90005], a[N], b[M];
signed main(){
ios::sync_with_stdio(0); cin.tie(0);
int n,m,k; cin>>n>>m>>k;
int tot = 0;
for(int i=1; i<=n; i++) cin>>a[i], tot+=a[i];
for(int i=1; i<=m; i++) cin>>b[i];
if(m<k) {cout<<"Impossible"; return 0;}
for(int i=1; i<=n; i++){
if(a[i] < k) {cout<<"Impossible"; return 0;}
}
memset(dp,-1,sizeof(dp));
dp[0][0] = 0;
for(int i=1; i<=m; i++){
for(int j=0; j<90005; j++){
dp[i][j] = dp[i-1][j];
if(j-b[i]>=0 and dp[i-1][j-b[i]] != -1){
dp[i][j] = max(dp[i][j], dp[i-1][j-b[i]] + min(b[i],n));
}
}
}
int ans = LLONG_MAX;
for(int i=tot; i<90005; i++){
if(dp[m][i] >= n*k) {ans = i-tot; break;}
}
if(ans == LLONG_MAX) cout<<"Impossible";
else cout<<ans;
return 0;
}
