백준 2839 설탕배달(DP, 그리디)

#백준 2839 설탕배달(DP)
#3 <= N <= 5000
N = int(input())

def min_num(N):
num = 0
while(True):
if(N % 5 != 0 and N >= 3):
N = N - 3
num += 1
if(N == 0):
break
elif(N % 5 == 0):
num += (N // 5)
break
if(N < 3):
return -1
return num

print(min_num(N))