from sys import stdin
n,m = map(int,input().split())
qw = [[0 for i in range(n+1)] for i in range(m+1)]
pppp = int(input())
c = set()
for i in range(pppp):
    a,b = map(int,stdin.readline().split())
    c.add((n+1)*(b-1)+a)


for i in range(m+1):
    for u in range(n+1):
        if u == i == 0:
            continue
        q = []
        if (n+1)*(i-1)+u in c:


            q.append(qw[i-1][u-1]+1)
        if i != 0:


            q.append(qw[i-1][u])
        if u != 0:


            q.append(qw[i][u-1])
        qw[i][u] = max(q)
print(int(round((n+m-max(q)*2)*100 + max(q) * (100**2+100**2)**0.5,0)))