from itertools import product

N=int(input())
X=0
for i in range(1,5):
    for T in product(range(10),repeat=i):
        if T[0]==0:
            continue

        x=""
        for t in T:
            x+=str(t)

        y=int(x+"0"*(9-i)+x[::-1])

        if y%(10**9+1)==0 and y<=N:
            X+=1
print(X)