package road;

import java.util.*;

import java.io.*;

public class Road {

private static ArrayList<Integer> number = new ArrayList<>();

private static void getData() throws IOException{

FileReader file = new FileReader("input.txt");

Scanner sc = new Scanner(file);

String str;

while (sc.hasNextLine()){

str = sc.nextLine();

StringTokenizer st = new StringTokenizer(str, " ");

while (st.hasMoreTokens()){

number.add(Integer.valueOf(st.nextToken()));

}

}

}

public static void main(String[] argv) throws IOException{

getData();

int roadCount = 0;

for(int i = 0; i < number.size(); i++){

if(i != 0){

if(number.get(i) == 1){

roadCount++;

}

}

}

roadCount = roadCount / 2;

PrintWriter pw = new PrintWriter(new File("output.txt"));

pw.print(String.valueOf(roadCount));

pw.close();

}

}