¿Cómo puedo editar mi fórmula para

weekday=(day+2(month)+3(month)/5+year+year/4-year/100+year/400)/7

para que no reciba un mensaje de error que diga "la expresión no se puede usar como una función"?

#include <iostream>
using namespace std;
int main()
{
int date=0;
int month=0;
int day=0;
int year=0;
int leftover=0;
int weekday=0;

cout<<"Enter Date (ex.20140912) :";
cin>>date;

year=date/10000;
leftover=date%10000;
month=leftover/100;
day=date%100;
{
if (month==3)
    {cout<<"March "<< day<<", "<< year<<":";
        weekday=(day+2(month)+3(month)/5+year+year/4-year/100+year/400)/7;

            if (weekday==0)
                {cout<<"Saturday";
                }
            if (weekday==1)
                {cout<<"Sunday";
                }
            if (weekday==2)
                {cout<<"Monday";
                }
            if (weekday==3)
                {cout<<"Tuesday";
                }
            if (weekday==4)
                {cout<<"Wednesday";
                }