#include<iostream> #include<algorithm> #include<cstdio> #include<queue> #include<stack> #include<cstring> using namespace std; char a[20]; int cnt=0; void dfs(int x){ if(x==16){ int nine=2; for(int i=1;i<=15;i++){ if(a[i]=='a')nine*=2; else nine--; if(nine<0)break; } if(nine==0)cnt++; return; } a[x]='a'; dfs(x+1); a[x]='b'; dfs(x+1); return; } int main(){ dfs(1); cout<<cnt; return 0; } /* #include<cstdio> freopen("文件名.in","r",stdin); freopen("文件名.out","w",stdout); */