import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		int suma = 0;
		int sumb = 0;
		int cnt = 0;
		for (int i = 1; i < n; i++) {
			String[] sa = br.readLine().split(" ");
			int a = Integer.parseInt(sa[0]);
			int b = Integer.parseInt(sa[1]);
			if (a > 0 || b > 0) {
				cnt++;
			}
			suma += a;
			sumb += b;
		}
		br.close();

		if (cnt <= 1) {
			System.out.println(1);
		} else {
			System.out.println(Math.max(suma, sumb) - Math.abs(suma - sumb) + 1);
		}
	}
}