#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define st first
#define nd second
#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(a) a.begin(), a.end()
const int MAXN = 307;
const int INF = 1e9;
int dp[MAXN * MAXN];
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n, m, k;
cin >> n >> m >> k;
int a[n];
int b[m];
rep(i, n) cin >> a[i];
rep(i, m) cin >> b[i];
sort(a, a + n);
rep(i, MAXN * MAXN) dp[i] = -INF;
dp[0] = 0;
rep(i, m) {
for (int j = MAXN * MAXN - 1; j >= b[i]; j--) {
dp[j] = max(dp[j], dp[j - b[i]] + min(n, b[i]));
}
}
int ans = INF;
int s = 0;
rep(i, n) s += a[i];
for (int x = s; x < (MAXN * MAXN); x++) {
if (dp[x] >= (k * n)) {
ans = x;
break;
}
}
if (ans == INF || a[0]<k) cout << "impossible" << '\n';
else cout << (ans - s) << '\n';
return 0;
}
