Pisi-brisi (pishi-brishi)

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main() {
    int n, m, k;
    cin >> n >> m >> k;

    stringstream ss;
    for (int i = n; i <= m; ++i) {
        ss << i;
    }

    string s = ss.str();
    int lengthReal = 0;

    for (int i = 1; i <= (signed)s.length(); ++i) {
        if (i % k != 0) {
            lengthReal++;
        }
    }

    cout << lengthReal;
}