623 B | 623 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
BLANK = " "
#inp = input
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
A, B = mii()
B = str(B)
crt = 1
for i in range(63):
if A < i:
if str(crt)[0] == B:
p(i)
break
crt *= 2
else:
p(0)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()