#include<iostream> #include<cstdio> #include<cstring> using namespace std; int main() { char s[256],stack[25],top=0; gets(s); for(int i=0;s[i]!='@';i++) { if(s[i]=='(') stack[top++]=s[i]; else if(s[i]-1==stack[top-1]) stack[--top]='\0'; } if(!top) cout<<"YES"; else cout<<"NO"; return 0; }