#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int n,cnt=0;
    cin>>n;
    for (int i = 1; i <= n; ++i)
    {
    int x = i;   
    while (x > 0) 
    {
        if (x % 10 == 1) 
            cnt++;  
        x = x / 10; 
    }
}
cout<<cnt;
    return 0;
}