console.log((args=>{
  const N = args|0;
  const e = Array(N+1).fill(1);
  e[0] = 0;
  for ( let i = 2; i <= N; i++ ) {
    for ( let j = i; j <= N; j+=i ) {
      e[j]++;
    }
  }
  return `${e.reduce((a,b,i)=>a+b*i)}`;
})(require('fs').readFileSync('/dev/stdin', 'utf8')));
