#include <iostream>
#include <vector>
using namespace std;
signed main()
{
ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// freopen("input.txt", "r", stdin);
int length, alphabet, requirements;
cin >> length >> alphabet >> requirements;
vector<int> dna(length);
for (int &nucleotide : dna) {
cin >> nucleotide;
}
int high = 0;
vector<int> requiers(alphabet);
while (requirements--) {
int nucleobase, require;
cin >> nucleobase >> require;
requiers[nucleobase] += require;
while (requiers[nucleobase] > 0) {
if (high == length) {
cout << "impossible";
return 0;
}
requiers[dna[high++]]--;
}
}
int res = length;
for (int low = 0; low < length; low++) {
res = min(res, high - low);
int nucleobase = dna[low];
requiers[nucleobase]++;
while (requiers[nucleobase] > 0) {
if (high == length) {
cout << res;
return 0;
}
requiers[dna[high++]]--;
}
}
cout << res;
return 0;
}
