#include <bits/stdc++.h>
using namespace std;
int solve();
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
const int MAXN = 1510;
const int INF = (int)1e9 + 10;
int a[MAXN];
pair<int, int> b[MAXN];
pair<int, int> segm[MAXN];
int dp[MAXN][MAXN];
int pref[MAXN];
int n, s, m, k;
bool check(int M) {
  for (int i = 1; i <= n; i++) {
    pref[i] = pref[i - 1];
    pref[i] += a[i] <= M;
  }
  memset(dp, 0, sizeof(dp));
  for (int i = 0; i < n; i++)
    for (int j = 0; j <= m; j++) {
      dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]);
      if (i < segm[i].second && j + 1 <= m) {
        dp[segm[i].second][j + 1] =
            max(dp[segm[i].second][j + 1],
                dp[i][j] + pref[segm[i].second] - pref[i]);
      }
    }
  return dp[n][m] >= k;
}
int solve() {
  cin >> n >> s >> m >> k;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= s; i++) cin >> b[i].first >> b[i].second;
  for (int i = 0; i <= n; i++) {
    for (int j = 1; j <= s; j++)
      if (b[j].first <= i + 1 && b[j].second > segm[i].second) segm[i] = b[j];
  }
  int L = 0, R = INF;
  while (L + 1 < R) {
    int M = (L + R) / 2;
    if (check(M))
      R = M;
    else
      L = M;
  }
  if (R == INF)
    cout << -1 << endl;
  else
    cout << R << endl;
  return 0;
}
