C. Hexadecimal's Numbers

題目連接：

http://www.codeforces.com/contest/9/problem/C

Description

One beautiful July morning a terrible thing happened in Mainframe: a mean virus Megabyte somehow got access to the memory of his not less mean sister Hexadecimal. He loaded there a huge amount of n different natural numbers from 1 to n to obtain total control over her energy.

But his plan failed. The reason for this was very simple: Hexadecimal didn't perceive any information, apart from numbers written in binary format. This means that if a number in a decimal representation contained characters apart from 0 and 1, it was not stored in the memory. Now Megabyte wants to know, how many numbers were loaded successfully.

Input

Input data contains the only number n (1?≤?n?≤?109).

Output

Output the only number — answer to the problem.

Sample Input

10

Sample Output

2

Hint

題意

問(wèn)你小于等于n的數(shù)里面，有多少個(gè)只由0和1組成的

題解：

感覺(jué)上沒(méi)多少個(gè)數(shù)嘛，那就直接dfs就好了啦

代碼

#include<bits/stdc++.h> using namespace std; long long n; map<int,int> vis; long long ans = 0; void dfs(long long x) {if(x>n)return;if(vis[x])return;vis[x]=1;ans++;dfs(x*10);dfs(x*10+1); } int main() {cin>>n;dfs(1);cout<<ans<<endl; }

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