#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define fs first
#define sc second
using namespace std;
const int N = 2e5 + 5;
int a[N], freq[N], b[N];
signed main(){
int n, k, rr;
cin >> n >> k >> rr;
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < rr; i++) {
int x, q;
cin >> x >> q;
b[x] = q;
}
int l = 0, r = 0;
int cnt = 0;
while (true) {
freq[a[r]]++;
if (freq[a[r]] == b[a[r]]) cnt++;
if (cnt == rr) break;
r++;
if (r == n) break;
}
if (cnt < rr) {
cout << "impossible" << endl;
return 0;
}
while (l <= r) {
if (freq[a[l]] == b[a[l]]) break;
freq[a[l]]--;
l++;
}
cout << r - l + 1 << endl;
}
