错排。中的阶乘要注意不能超过20，不然longlong也救不了

#include<stdio.h>int main(){    int n,i;    long long a[15];    a[1]=0;    a[2]=1;    for (i = 3;i < 15;i ++)        a[i] = (i-1)*(a[i-1]+a[i-2]);    scanf("%d",&n);    while (n){        int m = n;        if (n%2==1)n = n/2;        else n = n/2;        int j,k;        long long mmsum = 0;        for (i = 0;i < n;i ++){//m = 5,n = 2            long long summ = 1,sumn = 1,summn = 1;            for (j = m-n+i+1;j <= m;j ++)                summ *= j;            for (j = 2;j <= n-i;j ++)                sumn *= j;            mmsum += summ/(sumn*summn)*a[n-i];        }//现在允许是已经错排的次数        printf("%lld\n",mmsum+1);        scanf("%d",&n);    }    return 0;}