1. #include <cstdio>
    2. #include <algorithm>
    3. #include <cstdlib>
    4. #include <cstring>
    5. #include <cmath>
    6. #include <iostream>
    7. using namespace std;
    8. inline int gi(){
    9.     char tmp=getchar();int ans=0;int flag=1;
    10.     while(!isdigit(tmp)) {
    11.         if(tmp=='-'){
    12.             flag=-1;
    13.             tmp=getchar();
    14.             break;
    15.         }
    16.         tmp=getchar();
    17.     }
    18.     while(isdigit(tmp)){
    19.         ans=ans*10+tmp-'0';
    20.         tmp=getchar();
    21.     }
    22.     return ans*flag;
    23. }
    24. struct Big{
    25.     int Num[3002],len;    
    26.     void init(){
    27.         len=1;memset(Num,0,sizeof Num);
    28.     }
    29.     void print(){
    30.         for(int i=len;i;--i)
    31.             printf("%d",Num[i]);
    32.         putchar('\n');
    33.     }
    34.     Big operator * (const int & b){
    35.         Big ans;
    36.         for(int i=1;i<=len;++i)
    37.              ans.Num[i]=Num[i];
    38.         ans.len=len+10;
    39.         for(int i=1;i<=len;++i){
    40.             int t=ans.Num[i]*b;
    41.             ans.Num[i]=t;
    42.         }
    43.         for(int i=1;i<=ans.len;++i)
    44.             ans.Num[i+1] += (ans.Num[i]/10),
    45.             ans.Num[i] = (ans.Num[i]%10);    
    46.         while(!ans.Num[ans.len--]); // 去除前导0
    47.         ans.len++;
    48.         return ans;
    49.     }
    50.     Big operator / (const int &b){    
    51.         Big ans=*this;
    52.         for(int i=ans.len;i;--i){
    53.             ans.Num[i-1]+=(ans.Num[i]%b)*10;
    54.             ans.Num[i]/=b;
    55.         }
    56.         while(!ans.Num[ans.len--]); // 去除前导0
    57.         ans.len++;
    58.         return ans;
    59.     }
    60. };
    61. int Degree[199239];
    62. signed main()    
    63. {
    64.     #ifndef ONLINE_JUDGE
    65.     freopen("data.in","r",stdin);
    66.     #endif
    67.     int n=gi();
    68.     int sum=0;
    69.     // test part =================================
    70.     /*
    71.     Big a;a.init();a.Num[1]=3;a.len=1;
    72.     for(int i=1;i<=20;++i){
    73.         a=a*3;
    74.         a.print();
    75.     }
    76.     for(int i=1;i<=20;++i)
    77.         a=a/3,a.print();
    78.     return 0;
    79.     // end test ===============================
    80.     */
    81.     Big Mul;Mul.init();Mul.Num[1]=1;Mul.len=1;
    82.     int k=0;
    83.     for(int i=1;i<=n;++i){
    84.         int p=gi();
    85.         Degree[i]=p;
    86.         if(p!=-1){
    87.             ++k;
    88.             sum+=p-1;
    89.         }
    90.     }
    91.     Big ans;
    92.     ans.init();
    93.     ans.Num[1]=1;ans.len=1;
    94.     for(int i=2;i<=n-2;++i)
    95.         ans=ans*i;    
    96.     for(int i=1;i<=n;++i){
    97.         for(int j=2;j<Degree[i];++j)
    98.             ans=ans/j;
    99.     }
    100.     for(int i=2;i<=n-sum-2;++i)
    101.         ans=ans/i;
    102.     for(int i=1;i<=n-sum-2;++i){
    103.         ans=ans*(n-k);
    104.     }
    105.     ans.print();
    106.     return 0;
    107. }