105. Div 3

time limit per test: 0.25 sec / memory limit per test: 4096 KB

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 (\(1\le N\le2^{31}-1\)).

Output

Write answer to the output.

Example(s)

Sample Input	Sample Output
4	2

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <sstream>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <ctime>

#define inf 0x3f3f3f3f
#define Inf 0x3FFFFFFFFFFFFFFFLL
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define Rep(i, n) for (int i = 1; i <= (n); ++i)
#define clr(x, a) memset(x, (a), sizeof x)
using namespace std;
typedef long long ll;

int main() {
  int n; scanf("%d", &n);
  printf("%d\n", n / 3 * 2 + (n % 3 == 2));
  return 0;
}