c语言编程题求1!+2!+···+n!

#include  <stdio.h>
int fac(int a){
    
    
     return a==1||a==0 ? a:(fac(a-1)-fac(a-2))*a+fac(a-1);
}
int main()
{
    
    
    int a;
    printf("请输入n:");
    scanf("%d",&a);
    printf("1!+2!+···+%d=%d!\n",a,fac(a));
    return 0;
}