// input
char c;
// '' or ``
int t = 0;
// char, not string
while (cin >> c)
{
    if (c == '"')
    {
        cout << (t ? "''" : "``");
        // 1 -> 0, 0 -> 1
        t = 1-t;
    }
    else
    {
        // \n, space, or other
        cout << c;
    }
}