function main(input) {
  input=input.trim();
const a = parseInt(input.split(" ")[0], 10);
if(a%3==0){
  console.log(Math.floor(a/3));
}else{
  console.log(Math.floor(a/3)+1);
}
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));

