def main():
    with open("factor.in", "r") as f:
        n = int(f.readline())
    
    res = [0]*(n+1)
    for d in range(1, n+1):
        for multiple in range(d, n+1, d):
            res[multiple] += d
    
    total = sum(res)
    with open("factor.out", "w") as f:
        f.write(f"{total}\n")

if __name__ == "__main__":
    main()