import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        try {
            int T = 1;
            for (int i = 0; i < T; ++i) {
                Runner runner = new Runner(br, bw);
                runner.run();
                runner.flush();
            }
            br.close();
            bw.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

class Solution {

    public int solution(int[][] records) {
        int count = 0;

        var bs = new BitSet(200_000 + 1);
        for (var r : records) {
            int id = r[0];
            boolean enter = r[1] > 0 ? true : false;
            if (bs.get(id) == enter)
                ++count;
            bs.set(id, enter);
        }
        count += bs.cardinality();
        
        return count;
    }
}

class Runner {
    final Reader reader;
    final BufferedWriter bw;
    final StringBuilder sb = new StringBuilder();

    final int[][] records; 

    Runner(BufferedReader br, BufferedWriter bw) {
        this.reader = new Reader(br);
        this.bw = bw;
        try {
            var N = reader.readInts()[0];
            records = new int[N][];
            for (int i = 0; i < N; i++) {
                records[i] = reader.readInts();
            }

            sb.ensureCapacity(20);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public void flush() {
        try {
            bw.write(sb.toString());
            bw.flush();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public void run() throws IOException {
        var sol = new Solution();
        var res = sol.solution(records);
        sb.append(res).append('\n');
    }
}

class Reader {
    private BufferedReader br;

    public Reader(BufferedReader br) {
        this.br = br;
    }

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

    public Stream<String> lines() throws IOException {
        return br.lines();
    }

    public String line() throws IOException {
        return br.readLine();
    }

    public int[] readInts() throws IOException {
        String[] tokens = br.readLine().split(" ");
        int[] ints = new int[tokens.length];
        for (int i = 0; i < tokens.length; ++i) {
            ints[i] = Integer.parseInt(tokens[i]);
        }
        return ints;
    }

    public List<Integer> readIntegers() throws IOException {
        String[] tokens = br.readLine().split(" ");
        var res = new ArrayList<Integer>(tokens.length);
        for (String token : tokens) {
            res.add(Integer.valueOf(token));
        }
        return res;
    }
}