#include <bits/stdc++.h>
using namespace std;
#define arr array
#define pii pair<int, int>
const int MX_N = 2e5 + 5, INF = 1e9;
int n;
arr<int, MX_N> vl, rq;
arr<int, MX_N> scr;
set<pii> ord;
void upd(int i, int x) {
ord.erase({scr[i], i});
scr[i] += x;
ord.insert({scr[i], i});
}
int cmp() {
for (int i = 1; i <= n; i++) scr[i] = -rq[i];
for (int i = 1; i <= n; i++) ord.insert({scr[i], i});
int ans = INF, r = 0;
for (int l = 1; l <= n; l++) {
while (r != n && (r < l || ord.begin()->first < 0)) {
r++;
upd(vl[r], 1);
}
if (ord.begin()->first >= 0) ans = min(ans, r - l + 1);
upd(vl[l], -1);
}
return ans;
}
int main() {
// freopen("mrt.in", "r", stdin);
int tmp1, tmp2; cin >> n >> tmp1 >> tmp2;
for (int i = 1; i <= n; i++) { cin >> vl[i]; vl[i]++; }
for (int i = 1; i <= tmp2; i++) { int x; cin >> x; cin >> rq[x + 1]; }
int ans = cmp();
if (ans == INF) cout << "impossible" << endl;
else cout << ans << endl;
}
