import sys
input = sys.stdin.readline

n=int(input())
count=0
for i in range(10**6+1):
    S=str(i)
    T=S+S[::-1]
    U=S+S[:-1][::-1]

    ANS=T+(9-len(T))*"0"+T[::-1]

    if 1<=int(ANS)<=n and int(ANS)%(10**9+1)==0:
        count+=1

    ANS=U+(9-len(U))*"0"+U[::-1]

    if 1<=int(ANS)<=n and int(ANS)%(10**9+1)==0:
        count+=1

print(count)