let N = Int(readLine()!)!

var dp: [Int] = .init(repeating: 0, count: N + 1)

for i in 1...N {
  var current = i
  while current <= N {
    dp[current] += 1
    current += i
  }
}
var sum = 0 
for i in 1...N {
  sum += i * dp[i]
}
print(sum)
