from bisect import bisect
X = [[] for _ in range(9)]

X[0] = [str(i) for i in range(1,10)]
X[1] = [str(i) * 2 for i in range(1,10)]
for i in range(1,8,2):
    for x in X[i]:
        for y in range(10):
            X[i+1].append(x[:i//2+1]+str(y)+x[i//2+1:])
            if i + 2 < 9:
                X[i+2].append(x[:i//2+1]+str(y)*2+x[i//2+1:])

Y = []
for i in range(9):
    for x in X[i]:
        Y.append(int(x))
Y.sort()
N = int(input()) // (10**9+1)
print(bisect(Y,N))