C :

#include <stdio.h>

void main(){
	int a[10][10];
	int i,n,j,x=0;
	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++){
		x=x+a[i][i]+a[i][n-i-1];
	}

	printf("%d",x);
}

C++ :

#include <bits/stdc++.h>
using namespace std;

int a[20][20],n,s;
int i,j;
int main() {
	cin>>n;
	for(i = 0;i < n;i++){
		for(j = 0;j < n;j++){
			cin>>a[i][j];
		}
	}
	
	for(i = 0;i < n;i++){
		//05 14 23 32 41 50
		s = s + a[i][i];
		s = s + a[i][n-i-1];
	}
	
	cout<<s;
}

Java :

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int s = 0 ;
		int[][] a = new int[n][n];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				a[i][j] = sc.nextInt();
			}
		}
		for (int i = 0; i < n; i++) {
				s = s + a[i][i];
				s = s + a[i][n-i-1];
		}
		System.out.println(s);

	}
}