// Starcraft 2 enjoyer //
#include <bits/stdc++.h>
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
using namespace std;
#define LSOne(X) ((X) & -(X))
const int N = 3e2 + 5;
const int M = 9e4 + 5;
const int B = 18;
const long long K = 2;
const int LG = 60;
const long long INF = 1e18 + 5;
const int C = 26;
const int MOD = 1e9 + 7;
int n, m, k, a[N], b[N], dp[2][M], sum;
inline void solve()
{
cin >> n >> m >> k;
sum = 0;
for (int x = 0; x < n; x++)
{
cin >> a[x];
sum += a[x];
}
for (int x = 0; x < m; x++)
{
cin >> b[x];
}
for (int x = 0; x < n; x++)
{
if (a[x] < k)
{
cout << "impossible\n";
return;
}
}
memset(dp, -1, sizeof(dp));
dp[0][0] = 0;
for (int x = 0; x < m; x++)
{
for (int y = 0; y < M - b[x]; y++)
{
if (dp[0][y] == -1)
continue;
dp[1][y + b[x]] = max(dp[1][y + b[x]], dp[0][y] + min(n, b[x]));
}
for (int y = 0; y < M; y++)
{
if (dp[0][y] == -1)
continue;
dp[1][y] = max(dp[1][y], dp[0][y]);
}
for(int y = 0; y < M; y++)
{
dp[0][y] = dp[1][y];
dp[1][y] = -1;
}
}
for(int x = sum; x < M; x++)
{
if(dp[0][x] >= k*n)
{
cout << x - sum;
return;
}
}
cout << "impossible";
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
for (int x = 1; x <= t; x++)
{
solve();
}
return 0;
}
