#include <bits/stdc++.h>
using ll = long long;
using namespace std;

vector<bool> vis;
vector<vector<ll>> szom;

void dfs(ll node){
	vis[node] = true;
	for (ll x : szom[node]){
		if (!vis[x]){
			dfs(x);
		}
	}
}

int main() {
	ll n, m, q; cin >> n >> m >> q;
	vis.resize(n+m+1, false);
	szom.resize(n+m+1);
	while (q--){
		ll r, c; cin >> r >> c;
		szom[r].push_back(c+n);
		szom[c+n].push_back(r);
	}
	ll comp = 0;
	for (int i = 1; i < n+m+1; i++){
		if (!vis[i]) { 
			dfs(i);
			comp++;
		}
	}
	cout << comp-1;
}