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