#include <iostream>
#include <map>

using namespace std;

map<int,int>vis;

long long ans = 0;

int n;

//深度搜索,模仿
void dfs(int 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;

    return 0;
}