Project Euler 19

#include <iostream≶
using namespace std;

int main()
{
    int conta=0;
    int a,y,dia=1,m,d;
    for(int A=1901; A<=2000; A++)
    {
        for(int M=1; M<=12; M++)
        {

            a=(14-M)/12;
            y=A-a;
            m=M+12*a-2;
            d=(dia+y+y/4-y/100+y/400+(31*m)/12)%7;
            if(d==0)
                conta++;
        }
    }
    cout<<conta<<endl;
    return 0;
}