include <bits/stdc++.h>

using namespace std; int a[2002][2002];

int main() {

int n, m, k;
cin >> n >> m >> k;
for (int i = 1; i <= m; i++) {
	int mx, my;
	cin >> mx >> my;
	a[mx][my] = 1;
}
while (k--) {
	int x, d;
	cin >> x >> d;
	if (d == 0)
		d = -1;
	for (int i = 1; i <= n; i++) {
		if (a[x][i] == 1) {
			a[x][i] = 0;
			d = -d;
			m--;
		}
		if (x == 1)
			d = 1;
		if (x == n)
			d = -1;
		x += d;
	}
}
cout << m;
return 0;

}