#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int m,n,s=0; cin>>n>>m; int a[n][m],b=0,c=m; for(int i=0;i<n;i++){ for(int j=0;j<n;j++){ cin>>a[i][j]; if(i==j||i+j==n-1){ s+=a[i][j]; } } } cout<<s; return 0; }