#include<iostream> #include<string.h> using namespace std; int main(){ char s[20],sum=0,i,flag=0; cin.getline(s,20); for(i=0;i<strlen(s);i++){ if((s[i]>='A' && s[i]<='Z') || (s[i]>='a' && s[i]<='z') || (s[i]>='0' && s[i]<='9') || s[i]=='_'){ }else{ flag=1; break; } } if(flag==0 && (s[0]<'0' || s[0]>'9')){ cout << "yes"; } else{ cout << "no"; } return 0; }