# coding utf-8

n = int(input())

# 1 ~ 9 -> 1<=n<=9
# 10 ~ 99 -> 10=n<=10+90*2
# 100 ~ 999 -> 10+90*2<=n<=10+90*2+900*3

if int(n/10) == 0:
    print(n)
else:
    amari = int(n % 10)
    sho = int(n/10)
    if int(amari%2) != 0:
        if int(sho%2) != 0:
            sho = 0
        else:
            sho = 1
        print(int(amari/2)+int(sho*5))
    else:
        print(int(sho/2)+int(sho%2))