#include <bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
using namespace std;
const int N = 2e5+1, INF = 1e9;
int n, k, rr;
int a[N];
int q[N];
int cur[N];
int main()
{
ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
cin >> n >> k >> rr;
for (int i = 1; i <= n; cin >> a[i++]);
for (int i = 1, b; i <= rr; cin >> b >> q[b], i++);
int sat = (q[a[1]] && ++cur[a[1]] == q[a[1]]);
int l = 1, r = 1;
int sol = INF;
while (l <= r && r <= n) {
//cerr << l << ' ' << r << endl;
if ((sat == rr && l < r) || r == n) {
if (sat == rr)
sol = min(sol, r-l+1);
cur[a[l]]--;
if (q[a[l]] && cur[a[l]] == q[a[l]]-1) sat--;
l++;
} else {
r++;
cur[a[r]]++;
if (q[a[r]] && cur[a[r]] == q[a[r]]) sat++;
}
}
cout << (sol == INF ? "impossible" : to_string(sol));
}
