AC

#include <iostream>
#include <string>
using namespace std;
int countOnes(int n) {
    int count = 0;
    for (int i = 1; i <= n; i++) {
        string numStr = to_string(i);
        for (char c : numStr) {
            if (c == '1') {
                count++;
            }
        }
    }
    return count;
}
int main() {
    int n;
    cin >> n;
    int onesCount = countOnes(n);
    cout << onesCount << endl;
    return 0;
}