תכנית בC# ושאני מריץ אותה בהתחלה הכל בסדר ובסוף הוא נותן לי שגיאה…

זאת התכנית אשמח לדעת איפה טעיתי..
……
{
class Program
{
static void Main(string[] args)
{
int y;
int i;
int countover;
int countmea;
int sum;
int a;
int n;
int gr1;
int gr2;
int gr3;
int gr4;
int gr5;
double memostu;
double memocla;
string name;
int schom;
int sumshi;
double memoshi;
int sumtal;
int countmeashi;
int countovershi;
int countnechshi;
sumshi = 0;
sumtal = 0;
countmeashi = 0;
countovershi = 0;
countnechshi = 0;
Console.WriteLine("enter number of class");
a = int.Parse(Console.ReadLine());
for (y = 1; y <= a; y++)
{
countmea = 0;
countover = 0;
sum = 0;
Console.WriteLine("enter number of student");
n = int.Parse(Console.ReadLine());
sumtal=sumtal+n;
for (i = 1; i <= n; i++)
{
Console.WriteLine("enter your name and 5 grades");
name = Console.ReadLine();
gr1 = int.Parse(Console.ReadLine());
gr2 = int.Parse(Console.ReadLine());
gr3 = int.Parse(Console.ReadLine());
gr4 = int.Parse(Console.ReadLine());
gr5 = int.Parse(Console.ReadLine());
schom = gr1 + gr2 + gr3 + gr4 + gr5;
memostu =(double) schom / 5;
Console.WriteLine("mispar sidori={0} name={1} grade1={2} grade2={3} grade3={4} grade4={5} grade5={6} memotza={7}", i, name, gr1, gr2, gr3, gr4, gr5, memostu);
if (memostu < 55)
{
Console.WriteLine("nechshal");
countnechshi++;
}
else
{
countover = countover + 1;
if (memostu < 80)
{
Console.WriteLine("good");
countovershi++;
}
else
{
if (memostu != 100)
Console.WriteLine("very good");
else
{
countmea = countmea + 1;
Console.WriteLine("meole");
countmeashi++;
}
}
}
sum = sum + schom;
sumshi = sumshi + schom;
}