# include<iostream> # include<iomanip> using namespace std; int main(){ int n,juzhen[101][101]={},sum=0; cin>>n; for(int i = 0; i < n; i++)for(int j = 0; j < n; j++){ cin>>juzhen[i][j]; if(i==j||i+j==n-1)sum+=juzhen[i][j]; } cout<<sum; return 0; }