#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define pb push_back
#define debug(x) cerr<<#x<<"="<<x<<endl
#define pq priority_queue
#define inf 1ll<<60
#define rep(i,a,b) for (ll i=a;i<(b);i++)
#define MP make_pair
#define SZ(x) (int(x.size()))
#define mod 1000000007
#define ALL(x) x.begin(),x.end()
#define endl "\n"
void inc(ll &a,ll b) {a=(a+b)%mod;}
void dec(ll &a,ll b) {a=(a-b+mod)%mod;}
int prod(ll a,ll b) {return ll(a)*ll(b)%mod;}
int lowbit(ll x) {return x&(-x);}
ll p0w(ll base,ll p) {ll ret=1;while(p>0){if (p%2ll==1ll) ret=ret*base%mod;base=base*base%mod;p/=2ll;}return ret;}
const ll maxn=222222;
ll cnt[maxn],a[maxn];
ll need[maxn];
vector<pll>tmp;
ll ans=inf;
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
//freopen("i.txt","r",stdin);
ll n,k,r;cin>>n>>k>>r;
rep(i,1,n+1)cin>>a[i];
rep(i,1,r+1){
ll x,y;cin>>x>>y;
tmp.pb(MP(x,y));
need[x]=y;
}
deque<ll>q;
rep(i,1,n+1){
q.pb(a[i]);
cnt[a[i]]++;
while(!q.empty() and cnt[q[0]]>need[q[0]]){
cnt[q[0]]--;
q.pop_front();
}
bool ok=true;
for(auto x:tmp){
if(cnt[x.fi]<x.se){
ok=false;
}
}
if(ok)ans=min(ans,(ll)SZ(q));
}
if(ans==inf)cout<<"impossible"<<endl;
else cout<<ans<<endl;
return 0;
}
