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import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;


public class kug {

	public static void main(String[] args) throws IOException {
		
		kug solver = new kug();
		solver.init();
		solver.solve();
	}
	
	private void init() {
		
	}
	
	private static class Segment implements Comparable<Segment> {
		
		int from;
		int to;
		int cost;

		public Segment(int from, int to, int cost) {
			super();
			this.from = from;
			this.to = to;
			this.cost = cost;
		}
		
		@Override
		public int compareTo(Segment s) {
			return this.cost - s.cost;
		}
		
		
	}
	
	boolean[][] visited;
	int[] left;
	int[] right;
	
	private void solve() throws IOException { 
		Reader in = new Reader(System.in);
		PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));
		
		
		
		int n = in.nextInt();
		Segment[] segs = new Segment[n * (n+1) / 2];
		int k = 0;
		visited = new boolean[n+1][n+1];
		for (int i = 0; i < n; i++) {
			for (int j = i; j < n; j++) {
				segs[k++] = new Segment(i,j+1,in.nextInt());
			}
		}
		Arrays.sort(segs);
		long r = 0;
		left = new int[n+1];
		right = new int[n+1];
		Arrays.fill(left, -1);
		Arrays.fill(right, -1);
		
		for (Segment s : segs) {
			if (check(s.from, s.to)) {
				r += s.cost;
			}
		}
		
		out.println(r);
		
		out.flush();
		out.close();
	}
	
	private boolean check(int from, int to) {
		if (visited[from][to]) return false;
		
		if (left[from] != -1) {
			if (left[from] < to) {
				visited[from][to] = true;
				return check(left[from], to);
			} else {
				int toNew = left[from];
				right[left[from]] = -1;
				left[from] = -1;				
				check(from,to);
				check(to, toNew);
				return true;
			}
		} else if (right[to] != -1) {
			if (right[to] > from) {
				visited[from][to] = true;
				return check(from, right[to]);
			} else {
				int fromNew = right[to];
				left[right[to]] = -1;
				right[to] = -1;
				check(fromNew, from);
				check(from, to);
				return true;
			}
		} else {
			visited[from][to] = true;
			left[from] = to;
			right[to] = from;
			return true;
		}
	}

	private static class Reader {
	    BufferedReader reader;
	    StringTokenizer tokenizer;

	    /** call this method to initialize reader for InputStream */
	    Reader(InputStream input) {
	        reader = new BufferedReader(
	                     new InputStreamReader(input) );
	        tokenizer = new StringTokenizer("");
	    }

	    public void skipLine() throws IOException {
			reader.readLine();
		}

		/** get next word */
	    public String next() throws IOException {
	        while ( ! tokenizer.hasMoreTokens() ) {
	            //TODO add check for eof if necessary
	            tokenizer = new StringTokenizer(
	                   reader.readLine() );
	        }
	        return tokenizer.nextToken();
	    }

	    public int nextInt() throws IOException {
	        return Integer.parseInt( next() );
	    }
	    
	    public double nextDouble() throws IOException {
	        return Double.parseDouble( next() );
	    }
	    
	    public long nextLong() throws IOException {
	    	return Long.parseLong(next());
	    }
	}
}