Div 3

Div 3

Time Limit:250MS     Memory Limit:4096KB     64bit IO Format:%I64d & %I64u

Submit Status

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<=2³¹ - 1).

Output

Write answer to the output.

Sample Input

4

Sample Output

2

#include
#include
using namespace std;
int main()
{
    int n,sum;
    while(scanf("%d",&n)!=EOF)
    {
       sum=n/3*2;
       if(n%3==2)sum++;
       printf("%d\n",sum);
    }
    return 0;
}