def main():
    n, m = map(int,raw_input().split())
    from math import sqrt
    a = [[0] * (n + 1) for i in range(m + 1)]
    b = [[0] * (n + 1) for i in range(m + 1)]
    e = sqrt(2) * 100
    k = int(raw_input())
    for i in range(k):
        x, y = map(int,raw_input().split())
        b[y][x] = 1
    a[0][0] = 0
    for i in range (1, n + 1):
        a[0][i] = a[0][i - 1] + 100
    for j in range(1, m + 1):
        a[j][0] = a[j - 1][0] + 100
    for i in range(1, m + 1):
        for j in range(1, n + 1):
            if b[i][j] == 1:
                a[i][j] = min(a[i - 1][j - 1] + e, a[i - 1][j] + 100, a[i][j - 1] + 100)
            else:
                a[i][j] = min(a[i - 1][j] + 100, a[i][j - 1] + 100)
    print(int(a[m][n]))
main()