// Source: https://usaco.guide/general/io

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

vector<bool> visited;
vector<vector<int>> elek;

void dfs(int v){
    visited[v]=true;
    for(int x: elek[v]){
        if(!visited[x]){
            dfs(x);
        }
    }
}


int main() {
	int n, m, q;cin>>n>>m>>q;
    elek.assign(n+m, vector<int> {});
    for(int i=0;i<q;i++){
  //      cout<<"Yes"<<endl;
        int x, y;cin>>x>>y;
        x--;y--;
        elek[x].push_back(y+n);
        elek[y+n].push_back(x);
    }
    visited.assign(n+m, false);
    int ans=0;
    for(int i=0;i<n+m;i++){
  //      cout<<visited[i]<<endl;
        if(!visited[i]){
            dfs(i);
            ans++;
  //          cout<<"YESSIR"<<endl;
        }else{
  //          cout<<"Yes"<<endl;
        }
    }
    ans--;
    cout<<ans<<'\n';
}