#/usr/bin/env python

from collections import defaultdict
import re

RE_CMD = re.compile(r"^\$ (ls|cd)(.*)$")
RE_LS_DIR = re.compile(r"^dir (.*)$")
RE_LS_FILE = re.compile(r"^(\d+) (.*)$")

sizes = defaultdict(int)
dir_cur = "/"
size_unused = 30000000
size_total = 70000000

with open("input.txt", "r") as f:
    for line in f:
        line = line.strip()
        m = RE_LS_FILE.match(line)
        if m:
            sizes[dir_cur] += int(m.group(1))
            continue
        m = RE_CMD.match(line)
        if m and m.group(1) == 'cd':
            cd_args = m.group(2).strip()
            if cd_args == '..':
                dir_cur = "/".join(dir_cur.split("/")[:-2])+"/"
            elif cd_args == "/":
                dir_cur = "/"
            else:
                dir_cur += cd_args + "/"
            continue

#not very optimal ;( recursion and tree build will be faster
sizes_total = defaultdict(int)
for dir in (sorted(sizes.keys(), key=len, reverse=True)):
    tokens = dir.split("/")[:-1]
    for i in range(1, len(tokens)+1):
        x = "/".join(tokens[:i])+"/"
        sizes_total[x] += sizes[dir]


size_required = size_unused - (size_total - sizes_total["/"])
print(min([x for x in sizes_total.values() if x >= size_required]))