Div 3

Problem Description

There is sequence 1, 12, 123, 1234, …, 12345678910, … . Given first N elements of that sequence. You must determine amount of numbers in it that are divisible by 3.

Input

Input contains N (1<=N<=2^31 - 1).

Output

Write answer to the output.

Sample Input

4

Sample Output

2

Solution

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#include <bits/stdc++.h>

int main() {
    std::ios::sync_with_stdio(false);
    int n{};
    std::cin >> n;
    std::cout << n / 3 * 2 + (n % 3 > 1) << std::endl;
    return 0;
}