#include <stdio.h>
#include <string.h>

int main()
{
	int top = -1,flag = 1;
	char s[1000];
	gets(s);
	char *p = s;
	while(*p != '\0')
	{
		if(*p == 'A')
			top++;
		else if(*p == 'D' && top > -1)
			top--;
		else if(*p == 'D' && top == -1)
		{
			flag = 0;
			break;
		}
		p++;
	}
	if(top == -1 && flag) printf("yes");
	else printf("no");
	return 0;
}