#include <bits/stdc++.h>
#define rep(i,j,n) for(register int i=j;i<=n;i++)
#define Rep(i,j,n) for(register int i=j;i>=n;i--)
#define low(x) x&(-x)
using namespace std ;
typedef long long LL ;
const int inf = INT_MAX >> 1 ;
inline LL In() { LL res(0) , f(1) ; register char c ;
#define gc c = getchar()
while(isspace(gc)) ; c == '-' ? f = - 1 , gc : 0 ;
while(res = (res << 1) + (res << 3) + (c & 15) , isdigit(gc)) ;
return res * f ;
#undef gc
}
string s ;
inline void Ot() {
getline(cin , s) ;//cin >> s ;
int len = s.length() ;
if(isdigit(s[0])) {
puts("no") ;
return ;
}
for(register int i=0;i<len;i++){
if(!isalpha(s[i]) and !isdigit(s[i]) and s[i] != '_') {
puts("no") ;
return ;
}
}
puts("yes") ;
}
signed main() {
// freopen("test.in","r",stdin) ;
return Ot() , 0 ;
}