Baekjoon 2839번(python)

kg = int(input())

count = kg // 5
kg = kg % 5

while True:
    if(kg % 3 == 0):
        count += kg // 3
        break
    
    count -= 1
    if(count < 0):
        count = -1
        break
        
    kg += 5
    
print(count)