#include <bits/stdc++.h>
using namespace std;
int barr[305], dp[305][305 * 305];
int main(){
int n, m, k; cin >> n >> m >> k;
int total = 0;
for (int i = 0; i < n; i++){
int a; cin >> a;
if (a < k){
cout << "Impossible\n";
return 0;
}
total += a;
}
for (int i = 0; i < m; i++) cin >> barr[i];
memset(dp, INT_MIN, sizeof(dp));
dp[0][barr[0]] = min(n, barr[0]);
for (int i = 1; i < m; i++){
for (int j = 0; j < 305 * 305; j++){
dp[i][j] = dp[i-1][j];
if (barr[i] <= j) dp[i][j] = max(dp[i][j], dp[i-1][j - barr[i]] + min(n, barr[i]));
}
}
bool pos = 0; int ans;
for (int i = total; i < 305 * 305; i++){
if (dp[m-1][i] >= n * k){
pos = 1;
ans = i;
break;
}
}
if (!pos) cout << "Impossible\n";
else cout << ans - total << '\n';
}
