package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var n, m, k int
	fmt.Fscan(in, &n, &m, &k)

	grid := make([]bool, (n+2)*(m+2))
	idx := func(x, y int) int { return x*(m+2) + y }

	for t := 1; t <= k; t++ {
		var i, j int
		fmt.Fscan(in, &i, &j)
		grid[idx(i, j)] = true
		for a := 0; a < 2; a++ {
			for b := 0; b < 2; b++ {
				x := i - a
				y := j - b
				if x >= 1 && y >= 1 && x+1 <= n && y+1 <= m {
					if grid[idx(x, y)] && grid[idx(x+1, y)] && grid[idx(x, y+1)] && grid[idx(x+1, y+1)] {
						fmt.Fprintln(out, t)
						return
					}
				}
			}
		}
	}
	fmt.Fprintln(out, 0)
}