C :

#include<stdio.h>
int main()
{
	int a[100][100];
	int n, i, j, b, k=0, f=0, sum;
	scanf("%d", &n);
	for(i=0; i<n; i++)
	{
		for(j=0; j<n; j++)
		{
			scanf("%d", &a[i][j]);

		}
	}
	
	for(i=0; i<n; i++)
	{
		k += a[i][i];
		
	}

	for(i=0,j=n-1; i<n && j>=0; i++, j--)
	{
		f += a[i][j]; 

	}
	b = n/2;
	sum = k + f;
	if(n %2 != 0)
	{
		sum = sum - a[b][b];
	}
	printf("%d", sum);
	return 0;

}

C++ :

#include<stdio.h>
int main()
{
	int a[100][100];
	int n, i, j, b, k=0, f=0, sum;
	scanf("%d", &n);
	for(i=0; i<n; i++)
	{
		for(j=0; j<n; j++)
		{
			scanf("%d", &a[i][j]);

		}
	}
	
	for(i=0; i<n; i++)
	{
		k += a[i][i];
		
	}

	for(i=0,j=n-1; i<n && j>=0; i++, j--)
	{
		f += a[i][j]; 

	}
	b = n/2;
	sum = k + f;
	if(n %2 != 0)
	{
		sum = sum - a[b][b];
	}
	printf("%d", sum);
	return 0;

}

Pascal :

var a:array[1..1000,1..1000] of longint;
    n,i,j,x1,x2,y1,y2,sum:longint;
begin
  read(n);
  for i:=1 to n do
    for j:=1 to n do
      read(a[i,j]);
  x1:=1; y1:=1;
  x2:=1; y2:=n;
  sum:=sum+a[x1,y1]+a[x2,y2];
  while (x1<n) and (y1<n) do
  begin
    inc(x1); inc(y1);
    sum:=sum+a[x1,y1];
  end;
  while (x2<n) and (y2>1) do
  begin
    inc(x2); dec(y2);
    sum:=sum+a[x2,y2];
  end;
  if n mod 2=1 then sum:=sum-a[n div 2+1,n div 2+1];
  writeln(sum);
end.