#include <iostream>
#include <algorithm>

using namespace std;

void urlify(string& s) {
    int space_quantity = count(s.begin(), s.end(), ' ');
    //ut << space_quantity;
    int i = s.size() - 1;
    s.resize(s.size() + 2 * space_quantity);
    int j = s.size() - 1;

    while (i >= 0) {
        if (s[i] == ' ') {
            s[j--] = '0';
            s[j--] = '2';
            s[j--] = '%';
        } else {
            s[j--] = s[i];
        }
        --i;
    }


}
int main() {
    {
        string s = "my url";
        urlify(s);
        cout << s << endl;
    }
    {
        string s = "     ";
        urlify(s);
        cout << s << endl;
    }
    {
        string s = "a a a a a";
        urlify(s);
        cout << s << endl;
    }
    {
        string s = "";
        urlify(s);
        cout << s << endl;
    }
    {
        string s = "ff ffd ff  ";
        urlify(s);
        cout << s << endl;
    }
    return 0;
}