process.stdin.resume();
process.stdin.setEncoding('utf8');
// 自分の得意な言語で
// Let's チャレンジ！！

var lines = [];
var reader = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});
reader.on('line', (line) => {
  lines.push(line);
});
reader.on('close', () => {
  const N = lines[0]-0;
  let ans = 0;
  for(let i=1;i<=N;i++){
      const cnt = (~~(N/i));
      ans += cnt*(cnt+1)/2*i;
  }
  console.log(ans.toString());
  
});
