/* Pattern is 0 1 1 0 1 1 0 1 1...
 * 0 for not divisible by 3
 * 1 for divisible by 3
 */
 
#include<cstdio>
 
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
		printf("%d\n",((n/3)<<1)+((n%3)-1>0?(n%3-1):0));
	return 0;
}