#include<iostream> #include<bits/stdc++.h> using namespace std; typedef long long ll; ll s[1001] int mian(){ s[1]=0; s[2]=1; for(int i=3;i<=1000;i++) { s[i]=(i-1)*(s[i-1]+s[i-2]); } int n; while(cin>>n) printf("%d\n",s[n]); return 0; } cout<<a[n]<<endl; return 0; }