include<stdio.h>

include<stdlib.h>

include<string.h>

char a[1005]; int main() { int c,f,j,g=0,i;char m; int count1=0,count2=0; gets(a); f=strlen(a); for(c='a';c++;c<='h') { m=c; for(i=0;i<=(f/2)-1;i++) { count1=count1+1; } j=0; for(strlen(a)-j-1;j<f/2;j++) { count2=count2+1; } if(count1==count2){ g=g+1; }

}if(g==26)
{
    printf("yes\n");
}
else
    printf("no\n");

return 0; }