#include<bits/stdc++.h>
using namespace std;
int a,b,n;
long long dp[100][100]={};
int main(){
	cin>>a>>b>>n;
	for(int i=0;i<n;i++){
		int x,y;
		cin>>y>>x;
		dp[x][y]=-1;
	}
	if(dp[1][1]==-1||dp[a][b]==-1){
		cout<<0;
		return 0;
	}
	dp[1][1]=1;
	for(int i=1;i<=b;i++){
		for(int j=1;j<=a;j++){
			if(dp[i][j]==-1) continue;
			if(i==1&&j==1)  continue;
			else if(dp[i][j-1]==-1&&dp[i-1][j]==-1)	dp[i][j]=-1;
			else if(i==1||dp[i-1][j]==-1)	dp[i][j]=dp[i][j-1];
			else if(j==1||dp[i][j-1]==-1)	dp[i][j]=dp[i-1][j];
			else dp[i][j]=dp[i-1][j]+dp[i][j-1];
		}
	}
	cout<<dp[b][a];
}