new gTotalRegisters, gTotalLogins;

// Under OnDialogResponse

// Your register dialog
if (dialogid == DIALOG_REGISTER)
{
    gTotalRegisters++;
    // Save gTotalRegisters according to your saving system
}

// Your login dialog
if (dialogid == DIALOG_LOGIN)
{
    gTotalLogins++;
    // Save gTotalLogins according to your saving system
}

public OnGameModeInit()
{
    // Load the value of total logins into gTotalLogins variable and same for gTotalRegisters..
}

new str[128];
format(str, sizeof(str), "%d players are registered with %d total successfull logins", gTotalRegisters, gTotalLogins);
// Send this where you want to