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Problems

# Degree of two

n degrees of number 2 are written sequentially in a line, i.e. the numbers from 2 to 2n without spaces. Find the value of n.

#### Input

n (1n1000) degrees of number 2 are written sequentially in a line.

#### Output

Print the value of n.

Time limit 1 second
Memory limit 128 MiB
Input example #1
248163264128

Output example #1
7