#include <bits/stdc++.h>
using namespace std;
void setIO(const string &name = "") {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  if (name.length()) {
    freopen((name + ".in").c_str(), "r", stdin);
    freopen((name + ".out").c_str(), "w", stdout);
  }
}
template <typename T>
void read(vector<T> &a) {
  for (auto &x : a) cin >> x;
}
template <typename T>
void read(vector<T> &a, long long n) {
  a.resize(n);
  for (auto &x : a) cin >> x;
}
template <class T, class U>
ostream &operator<<(ostream &out, const pair<T, U> &v) {
  out << "(";
  out << v.first << "," << v.second;
  return out << ")";
}
template <class T>
ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (auto(i) = 0; (i) < ((long long)(v).size()); (i)++) {
    if (i) out << ", ";
    out << v[i];
  }
  return out << "]";
}
template <typename T>
void print(vector<T> &a) {
  for (const auto &x : a) cout << x << ' ';
  cout << '\n';
}
void MOD(long long &x, long long m = 1000000007) {
  x %= m;
  if (x < 0) x += m;
}
template <typename T>
void dbg(const char *name, T &&arg1) {
  cout << name << " : " << arg1 << '\n';
}
template <typename T, typename... U>
void dbg(const char *names, T &&arg1, U &&...args) {
  const char *comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  dbg(comma + 1, args...);
}
template <class T>
void read(T &x) {
  cin >> x;
}
template <class T, class... U>
void read(T &t, U &...u) {
  read(t);
  read(u...);
}
long long gcd(long long a, long long b) { return !a ? b : gcd(b % a, a); }
struct dsu {
  vector<long long> link;
  vector<long long> size;
  long long num_comp = 1;
  void init(long long n) {
    link.assign(n, 0LL);
    size.assign(n, 1);
    num_comp = n;
    for (auto(i) = 0; (i) < (n); (i)++) link[i] = i;
  }
  long long find(long long x) {
    while (x != link[x]) x = link[x];
    return x;
  }
  bool same(long long a, long long b) { return find(a) == find(b); }
  void unite(long long a, long long b) {
    a = find(a);
    b = find(b);
    if (a == b) return;
    if (size[a] < size[b]) swap(a, b);
    size[a] += size[b];
    link[b] = a;
    num_comp--;
  }
};
long long n, m, q;
dsu graph;
int32_t main() {
  setIO();
  read(n, m, q);
  graph.init(n + m);
  for (auto(_) = 0; (_) < (q); (_)++) {
    long long a, b;
    read(a, b);
    --a, --b;
    b += n;
    graph.unite(a, b);
  }
  cout << graph.num_comp - 1 << '\n';
  return 0;
}
