n = int(input())
phi = list(range(n + 1))
ans = n * (n - 1) // 2
for i in range(2, n + 1):
    if phi[i] == i:
        for j in range(i, n + 1, i):
            phi[j] -= phi[j] // i
    ans -= phi[i] + n // i - 1
print(ans)