#include <stdio.h>

typedef struct {
	int key, id;
} data;

typedef struct {
	data obj[200001];
	int size;
} min_heap;

void push(min_heap* h, data x)
{
	int i = ++(h->size), j = i >> 1;
	data tmp;
	h->obj[i] = x;
	while (j > 0) {
		if (h->obj[i].key < h->obj[j].key) {
			tmp = h->obj[j];
			h->obj[j] = h->obj[i];
			h->obj[i] = tmp;
			i = j;
			j >>= 1;
		} else break;
	}
}

data pop(min_heap* h)
{
	int i = 1, j = 2;
	data output = h->obj[1], tmp;
	h->obj[1] = h->obj[(h->size)--];
	while (j <= h->size) {
		if (j < h->size && h->obj[j^1].key < h->obj[j].key) j ^= 1;
		if (h->obj[j].key < h->obj[i].key) {
			tmp = h->obj[j];
			h->obj[j] = h->obj[i];
			h->obj[i] = tmp;
			i = j;
			j <<= 1;
		} else break;
	}
	return output;
}

void chmin(int *a, int b)
{
	if (*a > b) *a = b;
}

void chmax(int *a, int b)
{
	if (*a < b) *a = b;
}

int main()
{
	int i, n, l[200001], r[200001];
	scanf("%d", &n);
	for (i = 1; i <= n; i++) scanf("%d %d", &(l[i]), &(r[i]));
	
	int k, L = 0, R = 1000000000, M;
	min_heap h[2];
	data d;
	while (L < R) {
		M = (L + R) / 2;
		h[0].size = 0;
		h[1].size = 0;
		for (i = 1; i <= n; i++) {
			d.key = l[i] - M;
			d.id = i;
			push(&(h[0]), d);
		}
		for (i = 1; i <= n; i++) {
			while (h[0].size > 0 && h[0].obj[1].key <= i) {
				d = pop(&(h[0]));
				d.key = r[d.id] - M;
				push(&(h[1]), d);
			}
			if (h[1].size == 0 || h[1].obj[1].key < i) break;
			pop(&(h[1]));
		}
		if (i <= n) {
			if (h[1].size == 0) L = M + 1;
			else R = M - 1;
		} else break;
	}
	if (L >= R) {
		printf("0\n");
		return 0;
	}
	
	L = 0;
	R = 1000000000;
	h[0].size = 0;
	h[1].size = 0;
	for (i = 1; i <= n; i++) {
		d.key = l[i];
		d.id = i;
		push(&(h[0]), d);
		d.key = r[i];
		d.id = i;
		push(&(h[1]), d);
	}
	for (i = 1; i <= n; i++) {
		d = pop(&(h[0]));
		chmax(&L, d.key - i);
		d = pop(&(h[1]));
		chmin(&R, d.key - i);
	}
	printf("%d\n", R - L + 1);
	fflush(stdout);
	return 0;
}