program grid_game
  implicit none
  integer :: h, w, n, p(200000,2) = 0, i, j = 1, x = 1, d
  read(*,*) h, w, n
  do i = 1, n
    read(*,*) p(i,:)
  end do
  call merge_sort(p(1:n,:))
  do i = 1, h
    do while (j <= n .and. p(j,1) < i+1)
      j = j+1
    end do
    d = 1
    do while (j <= n .and. p(j,1) == i+1)
      if (p(j,2) <= x) then
        write(*,'(i0)') i
        stop
      else if (p(j,2) == x+1) then
        d = 0
      end if
      j = j+1
    end do
    x = x+d
  end do
  write(*,'(i0)') h
contains
  subroutine merge_sort(a)
    integer, intent(inout) :: a(:,:)
    integer :: n, m, l, i, u
    n = size(a,1)
    m = n
    l = 1
    do while (m > 1)
      do i = 1, m/2
        u = min(2*i*l,n)
        call merger(a(2*(i-1)*l+1:(2*i-1)*l,:),a((2*i-1)*l+1:u,:))
      end do
      l = 2*l
      m = (m+1)/2
    end do
  end
  subroutine merger(a1,a2)
    integer, intent(inout) :: a1(:,:), a2(:,:)
    integer :: a(size(a1,1)+size(a2,1),size(a1,2))
    integer :: i1, i2, n1, n2
    i1 = 1
    i2 = 1
    n1 = size(a1,1)
    n2 = size(a2,1)
    do while (i1 <= n1 .and. i2 <= n2)
      if (a1(i1,1) < a2(i2,1) .or. &
      & (a1(i1,1) == a2(i2,1) .and. a1(i1,2) < a2(i2,2))) then
        a(i1+i2-1,:) = a1(i1,:)
        i1 = i1+1
      else
        a(i1+i2-1,:) = a2(i2,:)
        i2 = i2+1
       end if
    end do
    if (i1 <= n1) then
      a(i1+i2-1:n1+n2,:) = a1(i1:n1,:)
    else
      a(i1+i2-1:n1+n2,:) = a2(i2:n2,:)
    end if
    a1 = a(1:n1,:)
    a2 = a(n1+1:n1+n2,:)
  end
end program grid_game