#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#define deb(...) logger(#__VA_ARGS__, __VA_ARGS__)
template<typename ...Args>
void logger(string vars, Args&&... values) {
cerr<<vars<<" = ";
string delim="";
(...,(cerr<<delim<<values,delim=", "));
cerr<<"\n";
}
#else
#define deb(...) logger(#__VA_ARGS__, __VA_ARGS__)
template<typename ...Args>
void logger(string vars, Args&&... values) {}
#endif
#define pb push_back
#define sz(x) (int)(x.size())
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<typename T> inline void maxa(T& a,T b){a=max(a,b);}
template<typename T> inline void mina(T& a,T b){a=min(a,b);}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int mxN=2e5+5; //make sure this is right
const int mod=1e9+7;
int dp[mxN][2];
int main(){
cin.sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#ifdef LOCAL
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
#endif
int n,m,k; cin>>n>>m>>k;
int tot=0; int bad=0;
for(int i=0;i<n;i++){
int a; cin>>a;
if(a<k)
bad=1;
tot+=a;
}
if(bad){
cout<<"Impossible\n";
return 0;
}
memset(dp,-1,sizeof(dp));
int lim=m<=15?tot+1000:2*tot;
dp[0][1]=0;
for(int i=0;i<m;i++){
int b; cin>>b;
for(int j=0;j<=lim;j++){
if(j>=b && ~dp[j-b][(i%2)^1])
dp[j][(i%2)]=dp[j-b][(i%2)^1]+min(n,b);
maxa(dp[j][(i%2)],dp[j][(i%2)^1]);
}
}
for(int i=tot;i<=lim;i++){
if(dp[i][(m-1)%2]>=k*n){
cout<<i-tot<<"\n";
return 0;
}
}
cout<<"Impossible\n";
}
