简单死了

#include<bits/stdc++.h>
using namespace std;
int main() {
    int n, sum = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int j = i;
        while (j > 0) {
            if (j % 10 == 1) sum++;
            j /= 10;
        }
    }
    cout << sum;
    return 0;
}