#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#define lnt long long
using namespace std;

const int maxN=100+5;
const int maxM=1000000+5;
int n,m,q,x,x1,y,y1,cnt=0;
bool Ais[maxM];
int kount;

int main()
{
	freopen("deleteit.in","r",stdin);
	freopen("deleteit.out","w",stdout);

	scanf("%d%d%d",&n,&m,&q);
	cnt=n*m;
	for(int t=0;t<q;t++)
	{
		scanf("%d%d%d%d",&x,&y,&x1,&y1);
		for(int i=x;i<=x1;i++)
		{
			int u=i*m;
			for(int j=y;j<=y1;j++) Ais[u+j]=1;
		}
		kount=0;
		for(int i=0;i<cnt;i++)
			if(Ais[i]==0) Ais[kount++]=0;
		cnt=kount;
	}
	cout<<kount;

	return 0;
}