640 B | 640 chars
import sys
from math import sqrt, pi, sin, factorial
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = " " : [*map(int,inp().split(x))]
mfi = lambda x = " " : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
n, m = mii()
box = sorted(mii())
key = sorted(list(set(mii())))
i = j = 0
ans = 0
while i < len(box) and j < len(key):
if box[i] == key[j]:
ans += 1
i += 1
elif box[i] < key[j]:
i += 1
else:
j += 1
return ans
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()
p(ret)