#include<stdio.h>
#include<string.h>
int main()
{
	int i,c,flag,k;
	char a[2000];
	while(scanf("%s",a)!=EOF)
	{flag=1;k=0;
		c=strlen(a);
		if(a[c/2]!='&'||c==1)
			flag=0;
		for(i=0;i<c/2;i++)
			if(a[i]!=a[c-i-1])
			{flag=0;break;}
		for(i=0;i<c;i++)
			if(a[i]<='z'&&a[i]>='a');
			else if(a[i]=='&')
			{k++;}
			else flag=0;
		if(flag&&k==1)
			printf("YES\n");
		else printf("NO\n");
	}
	return 0;
}
/**************************************************************
	Problem: 2225
	User: admin
	Language: C
	Result: Accepted
	Time:56 ms
	Memory:1144 kb
****************************************************************/