import numpy as np
n = int(input())
sieve = np.ones(n*3+1, dtype=bool)
for i in range(2, int((n*3)**0.5)+2):
    if sieve[i]:
        sieve[i+i::i] = False
ps1 = np.where(sieve)[0][2:]
ps2 = ps1[ps1 <= n]
cnt = np.zeros(n*3+1, dtype='int64')
res = 0
for i in reversed(range(len(ps2))):
    a = ps2[i]
    res += cnt[ps1 - a].sum()
    cnt[ps2[i+1:] + a] += 1
print(res)