public class TestParens
{
	public static void main(String[] args)
	{
		int excess=0;
			
		if(args.length<1)
		{
			System.out.println("Not enough arguments.");
			System.exit(0);
		}
		else
		{
			String testString=args[0];
			for(int j=0;j<testString.length();j++)
			{
				if(testString.charAt(j)=='{')
					excess++;
				else if(testString.charAt(j)=='}')
					excess--;
				if(excess<0)
				{
					System.out.println("no");
					System.exit(0);
				}
			}
		}
		if(excess==0)
			System.out.println("yes");
		else
			System.out.println("no");
	}
}