Practice Magical String

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#481

LeetCode Problem

Magical String

Two Pointers String

Problem Statement

A magical string s consists of only '1' and '2' and obeys the following rules: The first few elements of s is s = "1221121221221121122……". If we group the consecutive 1's and 2's in s, it will be "1 22 11 2 1 22 1 22 11 2 11 22 ......" and the occurrences of 1's or 2's in each group are "1 2 2 1 1 2 1 2 2 1 2 2 ......". You can see that the occurrence sequence is s itself. Given an integer n, return the number of 1's in the first n number in the magical string s.

Source: Magical String on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

n = 6

Output

# Example 2

Input

n = 1

Output

Constraints

1 <= n <= 10^5

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