#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

bool checkin(char c){
    if(c >= 'A' && c <= 'Z') return true;
    if(c >= 'a' && c <= 'z') return true;
    if(c >= '0' && c <= '9') return true;
    if(c == '_') return true;
    return false;
}

bool check(char* arr){
    if(arr == NULL) return false;
    int p = 0;
    if(arr[0] >= '0' && arr[0] <= '9') return false;
    while(arr[p] != '\0' && arr[p] != '\n'){
        //if(arr[p] == '\n') continue;
        if(!checkin(arr[p])) return false;
        p++;
    }
    return true;
}



int main(){                     /* is main */
    char arr[22];
    fgets(arr, 22, stdin);
    printf(check(arr) ? "yes\n" : "no\n");
    return 0;
}