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[] a = new int[n];
		int[] b = new int[n];
		int xa = 0;
		int xb = 0;
		for (int i = 1; i < n; i++) {
			String[] sa = br.readLine().split(" ");
			a[i] = Integer.parseInt(sa[0]);
			b[i] = Integer.parseInt(sa[1]);
			xa += a[i];
			xb += b[i];
		}
		br.close();

		a[0] = xb;
		b[0] = xa;

		int ans = 0;
		while (a[0] >= 0 && b[0] >= 0) {
			boolean flg = true;
			for (int i = 0; i < n; i++) {
				xa = 0;
				xb = 0;
				for (int j = 0; j < n; j++) {
					if (i != j) {
						xa += a[j];
						xb += b[j];
					}
				}
				if (xa < b[i] || xb < a[i]) {
					flg = false;
					break;
				}
			}
			if (flg) {
				ans++;
				a[0]--;
				b[0]--;
			} else {
				break;
			}
		}
		System.out.println(ans);
	}
}