UICKeyChainStore *keychain = [UICKeyChainStore keyChainStore];
NSString *username = @"kishikawakatsumi@mac.com";
NSString *password = keychain[username];
if (password) {
    // If found password in the Keychain,
    // then go to second page

}
else {
    // If not found password in the Keychain,
    // then go to initial login page
    UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"Main" bundle: nil];
    InitialViewController *initialVC = (InitialViewController*)[mainStoryboard instantiateViewControllerWithIdentifier: @"InitialVC"];
    self.window.rootViewController = initialVC;
}