有点长

#include<iostream>
using namespace std;


int main()
{
    int n,sum;
    cin >> n;
    for(int i = 1;i <= n;i++){
        int x = i;
        while(x != 0){
            if(x%10 == 1){
                sum++;
            }
            x /= 10;
        }
    }
    cout << sum;
    return 0;
}