#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#include <utility>
#include <iomanip>

using namespace std;

int main()
{
    ifstream in("padure2.in");
    ofstream out("padure2.out");

    std::set< std::pair<int, int> > mushrooms;
    int N, M, C;
    in >> N >> M >> C;
    for (int i = 0; i < C; ++i) {
        int x, y;
        in >> x >> y;
        mushrooms.insert({ x, y });
    }

    std::vector<int> currentLine(M + 1000);
    for (int i = 1; i <= M; ++i) {
        if (mushrooms.count({ 1, i }) > 0) {
            break;
        }
        currentLine[i] = 1;
    }

    for (int ln = 2; ln <= N; ++ln) {
        for (int i = 1; i <= M; ++i) {
            if (mushrooms.count({ ln, i }) == 0) {
                currentLine[i] += currentLine[i - 1];
            }
            else {
                currentLine[i] = 0;
            }
        }
    }

    out << currentLine[M] << endl;
    return 0;
}