#include <bits/stdc++.h>
#define int long long
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
const int N = 2e5+5, MOD = 1e9+7;
int val[N], cnt[N], arr[N];
int ans = 0;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int fastpow(int n, int p){
int res = 1;
while(p){
if(p&1) res = res * n % MOD;
n = n * n % MOD;
p >>= 1;
}
return res;
}
int hsh(int x){
if(cnt[x] <= 0) return 0;
return cnt[x] * val[x];
}
bool check(int x){
int tmp = ans;
ans = ((ans-hsh(x))%MOD+MOD)%MOD;
cnt[x]--;
ans = ((ans+hsh(x))%MOD+MOD)%MOD;
bool ok = (ans!=0);
cnt[x]++;
ans = tmp;
return ok;
}
signed main(){
fastio
int n,k,R;
cin >> n >> k >> R;
for(int i = 0;i < n;i++){
cin >> arr[i];
}
for(int i = 0;i < R;i++){
int x;
cin >> x;
val[x] = uniform_int_distribution<int>(0,1e9)(rng);
cin >> cnt[x];
ans += hsh(x);
}
int l = 0, r = -1, res = 1e18;
while(l < n){
while(r + 1 < n && check(arr[r+1])){
ans = ((ans-hsh(arr[r+1]))%MOD+MOD)%MOD;
cnt[arr[r+1]]--;
ans = ((ans+hsh(arr[r+1]))%MOD+MOD)%MOD;
r++;
}
if(r+1 < n&&!check(arr[r+1])){
res = min(res,r-l+2);
}
ans = ((ans-hsh(arr[l]))%MOD+MOD)%MOD;
cnt[arr[l]]++;
ans = ((ans+hsh(arr[l]))%MOD+MOD)%MOD;
l++;
}
if(res==1e18) cout << "impossible\n";
else cout << res << "\n";
}
