#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;

int m, n, q;
int X1, Y1, X2, Y2;
int h, yu, flag=0, cnt;

int main() {
	freopen("deleteit.in", "r", stdin);
	freopen("deleteit.out", "w", stdout);
	scanf("%d%d%d", &n, &m, &q);
	cnt=m*n;
	h=n-1; yu=m;
	for(int i=1; i<=q; i++) {
		scanf("%d%d%d%d", &X1, &Y1, &X2, &Y2);
		if(flag) {
			printf("0\n"); return 0;
		}
		X2=min(X2, h);
		int jian=(X2-X1+1)*(Y2-Y1+1);
		cnt-=jian;
		if(X2==h) {
			if(Y1>yu-1) cnt+=Y2-Y1+1;
			else cnt+=Y2-yu+1;
		}
		h=cnt/m; yu=cnt%m;
		if(yu==0) {h--; yu=m;}
		if(h<=0 && yu<=0) flag=1;
	}
	if(flag) printf("0\n");
	else printf("%d\n", h*m+yu);
	return 0;
}