fs = require('fs');
input = fs.readFileSync('/dev/stdin','utf8');
N = parseInt(input,10);
r = BigInt(0);
for(i = 1; i <= N; i++) {
  r = r + BigInt(i * c(i));
}
console.log((r + '').replace('n',''));
function c(n){
  d = 1;
  for(j = 2;j <= n; j++) {
    if(n % j == 0) d = d + 1;
  }
  return d;
}
