#include <iostream>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <time.h>
#include <stdlib.h>
#include <string>
#include <bitset>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <algorithm>
#include <sstream>
#include <stack>
#include <iomanip>
using namespace std;
#define pb push_back
#define mp make_pair
typedef pair<int,int> pii;
typedef long long ll;
typedef double ld;
typedef vector<int> vi;
#define fi first
#define se second
#define fe first
#define FO(x) {freopen(#x".in","r",stdin);freopen(#x".out","w",stdout);}
#define Edg int M=0,fst[SZ],vb[SZ],nxt[SZ];void ad_de(int a,int b){++M;nxt[M]=fst[a];fst[a]=M;vb[M]=b;}void adde(int a,int b){ad_de(a,b);ad_de(b,a);}
#define Edgc int M=0,fst[SZ],vb[SZ],nxt[SZ],vc[SZ];void ad_de(int a,int b,int c){++M;nxt[M]=fst[a];fst[a]=M;vb[M]=b;vc[M]=c;}void adde(int a,int b,int c){ad_de(a,b,c);ad_de(b,a,c);}
#define es(x,e) (int e=fst[x];e;e=nxt[e])
#define esb(x,e,b) (int e=fst[x],b=vb[e];e;e=nxt[e],b=vb[e])
#define SZ 888888
int ff[SZ];
int gf(int x) {return (~ff[x])?ff[x]=gf(ff[x]):x;}
void ini(int n) {memset(ff,-1,sizeof(ff[0])*(n+1));}
bool uni(int a,int b)
{
	a=gf(a),b=gf(b);
	if(a!=b) return ff[a]=b,1;
	return 0;
}
map<int,int> is;
int gs[SZ],gn=0;
int gid(int x)
{
	int&p=is[x];
	if(!p) gs[p=++gn]=x,ff[gn]=-1;
	return p;
}
ll solve(int n,int p,const vector<pii>& ex)
{
	p%=n;
	if(!p)
	{
		if(n>int(ex.size())+3) return 1e15;
		ini(n);
		for(unsigned _=0;_<ex.size();++_)
			uni(ex[_].fi,ex[_].se);
		for(int i=1;i<n;++i)
			if(gf(i)!=gf(0)) return 1e15;
		return 0;
	}
	bool chk=1;
	if(p<=int(ex.size())+3)
	{
		ini(p);
		for(unsigned _=0;_<ex.size();++_)
			uni(ex[_].fi%p,ex[_].se%p);
		for(int i=1;i<p;++i)
			if(gf(i)!=gf(0)) chk=0;
		if(chk)
		{
			int l=max(n-int(ex.size())-3,0),r=n-p;
			while(l<r)
			{
				int m=(l+r)>>1; gn=0; is.clear();
				for(int i=0;i<p;++i) gid(i);
				for(int i=m;i<n;++i) gid(i);
				for(unsigned _=0;_<ex.size();++_)
					uni(gid(ex[_].fi),gid(ex[_].se));
				for(int i=gn;i;--i) if(gs[i]<m+p)
					uni(gid(gs[i]),gid(gs[i]%p));
				bool go=1;
				for(int i=1;i<=gn;++i)
					if(gf(i)!=gf(1)) go=0;
				if(go) r=m; else l=m+1;
			}
			return l;
		}
	}
	vector<pii> nx;
	for(unsigned _=0;_<ex.size();++_)
		nx.pb(pii(ex[_].fi%p,ex[_].se%p));
	return solve(p,n,nx)+n-p;
}
ll main_()
{
	int n,m,k;
	cin>>n>>m>>k;
	vector<pii> s,s0;
	for(int i=1;i<=k;++i)
	{
		int a,b;
		cin>>a>>b;
		if(n>m) s.pb(pii(b%m,a%m)),s0.pb(pii(b,a));
		else s.pb(pii(a%n,b%n)),s0.pb(pii(a,b));
	}
	if(n>m) swap(n,m);
	if(n>k+10)
		return m+solve(n,m,s);
	if(m>3*k+40)
	{
		ll w=solve(m,n,s0);
		if(w<=m-n) return w+n;
		else return m+solve(n,m,s);
	}
	ini(n+m+3); int su=0;
	for(unsigned _=0;_<s0.size();++_)
	{
		int a=s0[_].fi,b=s0[_].se;
		su+=uni(a+1,b+n+1);
	}
	int c=0;
	while(su<n+m-1)
	{ 
		su+=uni(c%n+1,c%m+n+1), ++c;
		if(c>10000000) return 1e15;
	}
	return c;
}
int main()
{ 
	ll x=main_();
	if(x>1e15) x=1e15;
	printf("%lld\n",x);
}