#include "bits/extc++.h"
using namespace std;
template <typename T>
void dbgh(const T& t) {
cerr << t << endl;
}
template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
cerr << t << " | ";
dbgh(u...);
}
#ifdef DEBUG
#define dbg(...) \
cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
<< ": "; \
dbgh(__VA_ARGS__)
#else
#define cerr \
if (false) \
cerr
#define dbg(...)
#endif
#define endl "\n"
#define long int64_t
#define sz(x) int((x).size())
void solve() {
int n, m, q;
cin >> n >> m >> q;
int arr[n];
for (auto& a : arr) {
cin >> a;
}
int req[m] {};
while (q--) {
int a, b;
cin >> a >> b;
req[a] = max(req[a], b);
}
int nxtv[m];
memset(nxtv, -1, sizeof(nxtv));
int nxt[n];
for (int i = n - 1; i >= 0; i--) {
nxt[i] = nxtv[arr[i]];
nxtv[arr[i]] = i;
}
int ptr[m], cans = 0;
for (int i = 0; i < m; i++) {
if (!req[i]) {
continue;
}
int j = nxtv[i];
for (int k = 1; k < req[i]; k++) {
j = j == -1 ? -1 : nxt[j];
}
if (j == -1) {
cout << "impossible" << endl;
return;
}
ptr[i] = j;
cans = max(cans, j);
}
int ans = cans + 1;
for (int i = 0; i < n; i++) {
if (req[arr[i]]) {
ptr[arr[i]] = nxt[ptr[arr[i]]];
if (ptr[arr[i]] == -1) {
break;
}
cans = max(cans, ptr[arr[i]]);
}
ans = min(ans, cans - i);
}
cout << ans << endl;
}
int main() {
cin.tie(nullptr);
ios_base::sync_with_stdio(false);
cin.exceptions(ios::failbit);
solve();
}
