#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
N = int(readline())
S = read().rstrip().decode()

# %%
S = S.replace('3', '')
S = S.replace('5', '')
S = S.replace('7', '')

answer = N - len(S)

# %%
stack = [0]
for x in map(int, S):
    if stack[-1] == 1:
        answer += 1
        stack.pop()
    elif stack[-2:] == [9, 9] and x == 1:
        answer += 1
        stack.pop()
        stack.pop()
    else:
        stack.append(x)

# %%
print(answer)