def euler_phi2(N):
    phi = list(range(N + 1))
    for x in range(2, N + 1):
        if phi[x] == x:
            for y in range(x, N + 1, x):
                phi[y] = phi[y] // x * (x - 1)
    return phi


N = int(input())
div = [0] * (N + 1)
ans = N * (N + 1) //2
for i in range(2, N + 1):
    for j in range(i, N + 1, i):
        div[j] += 1

print(ans - sum(div) - sum(euler_phi2(N)))