import java.io.InputStream;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;

import static java.util.Comparator.*;

public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        Solver solver = new Solver(System.in, out);
        solver.solve();
        out.close();
    }
}
class Solver {
	Scanner sc;
	PrintWriter out;
    public Solver(InputStream in, PrintWriter out) {
    	sc = new Scanner(in);
    	this.out = out;
    }
    // ==================================================================
    public void solve() {
    	int N = Integer.parseInt(sc.next());
    	int[] A = new int[N];
    	int[] B = new int[N];
    	int sumA = 0, sumB = 0;
    	for (int i = 0; i < N -1 ; i++) {
			A[i] = Integer.parseInt(sc.next());
			B[i] = Integer.parseInt(sc.next());
			sumA += A[i];
			sumB += B[i];
		}
    	int a1, b1, sa, ans = 0;
    	boolean flg;
    	if(sumA >= sumB) {
    		sa = sumA - sumB;
    		a1 = 0;
    		for (; a1 <= sumB; a1++) {
				b1 = a1 + sa;
				flg = true;
				for (int j = 0; j < N - 1; j++) {
					if(A[j] > b1 + sumB - B[j] || B[j] > a1 + sumA - A[j]) {
						flg = false;	break;
					}
				}
				if(flg)		ans++;
			}
    	} else {
    		sa = sumB - sumA;
    		b1 = 0;
    		for (; b1 <= sumA; b1++) {
				a1 = b1 + sa;
				flg = true;
				for (int j = 0; j < N - 1; j++) {
					if(A[j] > b1 + sumB - B[j] || B[j] > a1 + sumA - A[j]) {
						flg = false;	break;
					}
				}
				if(flg)		ans++;
			}
    	}
    	out.println(ans);
    }
    // ==================================================================
}
class PP{
	public int key, val;
	public PP(int key, int val) {
		this.key = key;
		this.val = val;
	}
	public int getKey() {
		return key;
	}
	public int getVal() {
		return val;
	}
}