import sys for line in sys.stdin: a = int(line.strip()) print((a - 1) // 3 * (1 + (a % 3 != 0)))
import java.util.Scanner;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
long n = in.nextLong();
int times = (n%3 == 0) ? 1:2;
System.out.println(((n-1)/3)*times);
}
} const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;
void async function () {
// Write your code here
while(line = await readline()){
let tokens = line.split(' ');
let n = parseInt(tokens[0]);
let left=3,right=n-1
if(n<=3){
console.log(0)
return 0
}
while(right %3!==0)
right--
let count = right/3
left = n-right
let res = left % 3==0?count:count*2
console.log(res)
}
}()