#include <stdio.h>

int main(void)
{
    char a[11];
    int i,j = 0;
    int flag,sum = 0;
	
    scanf("%s", a);
	
    while(i < 11){
        while(j < 11){
            if(a[i] == a[j]){sum++;}
        }
        if(sum >= 2){
            flag = 1;
            break;
        }
    }
    if(flag == 1){
        printf("NO\n");
    }
    else{
        printf("YES\n");
    }
}