#include<stdio.h>
int factorial (int num)
{
    int fact=1;
    for(int i=1;i<=num;i++)
    {
        fact*=i;
    }
    return fact;
}
int main(){
    int n;
    scanf("%d",&n);
    if(n<=0){
        printf("Invalid Input");
        return 0;
    }
    int num, result=0;
    for(int i=o;i<n;i++)
    {
        scanf("%d",&num):
        if(num<=0){
            printf("Invalid Input");
            return 0;
        }
        int fact = factorial(num);
        if(num%2==0)
        result-=fact;
        else
        result+=fact;
    }
    printf("%d",result);
    }