# https://yukicoder.me/problems/no/1986

N = int(input())
# 美味しい:1 , 普通:0
candy = [1 if i % 2 == 0 else 0 for i in range(N)]
# print(candy)
F = []
S = []
for i, x in enumerate(reversed(candy)):
    if i % 2 == 1:
        F.append(x)
    else:
        S.append(x)
print(len(F))