control reaches end of non-void function [-Werror=return-type]

Even after using default else statement I am getting this error

int max_of_four(int a, int b, int c, int d)
{if((a>b)&&(a>c))
{        if(a>d)
        return a;
}
else if((b>c)&&(b>d))
{  return b; }
else if(c>d)
 { return c; }
else 
    return d;
}