P = list(range(20000+1))
P[0] = 0
P[1] = 0
for i in range(2,20000+1):
    if i*i>20000:break
    for j in range(i*i,20000+1,i):
        P[j] = P[i]
Q = []
for i in range(2,20000+1):
    if P[i]==i:
        Q.append(i)
N = len(Q)
Q = [0]+Q
M = int(input())
INFTY = 10**5
dp = [[-INFTY for _ in range(M+1)] for _ in range(N+1)]
for i in range(N+1):
    dp[i][0] = 0
if M>1:
    dp[1][2] = 1
for i in range(2,N+1):
    for j in range(M+1):
        dp[i][j] = dp[i-1][j]
        if j>=Q[i]:
            dp[i][j] = max(dp[i][j],dp[i-1][j-Q[i]]+1)
if dp[N][M]<=0:
    print(-1)
else:
    print(dp[N][M])