n = int(input())
c = 0
# 循环1~n
for i in range(1, n + 1):
    # 对每个1~n的数拆位,看有多少个1,c+=1
    while i > 0:
        s = i % 10
        if s == 1:
            c += 1
        i //= 10
print(c)
/**************************************************************
	Problem: 1448
	User: admin
	Language: Python
	Result: Accepted
	Time:217 ms
	Memory:34244 kb
****************************************************************/