f(n,t){return n?t=pow(10,t=log10(n)),f(n%t)*10+n/t:0;}long n;main(m){scanf("%ld",&n);m=log10(n/=1+1e9);printf("%d",n=n/pow(10,-~m/2)-~(m%2*9)*pow(10,m/2)-2+(n<=f(n)));}