## https://yukicoder.me/problems/no/2552




def main():
    N = int(input())

    dp = [0] * (N + 1)

    answer = 0
    for p in reversed(range(2, N + 1)):

        x = N // p
        x = x * x

        q = 2 * p
        while q <= N:
            x -= dp[q]
            q += p
        
        dp[p] = x

        y = x - (2 * (N // p) - 1)
        y //= 2
        answer += y
    print(answer)
        



if __name__ == "__main__":
    main()