#include <iostream>
#include <algorithm>

using namespace std;

int n, L;

struct RQzourun
{
	int l, r;
} a[25005];

int solve()
{
	int nowfar = a[1].r, cnt = 1, i = 2;
	if (a[1].l > 1) return -1;
	if (nowfar >= L) return cnt;
	while (nowfar < L)
	{
		int mr = -1;
		for (; i <= n && a[i].l <= nowfar; i ++ )
		{
			mr = max(mr, a[i].r);
		}
		if (mr <= nowfar) return -1;
		cnt ++ ;
		nowfar = mr;
		if (nowfar >= L) return cnt;
	}
	return nowfar >= L ? cnt : -1;
}

bool cmp(RQzourun a, RQzourun b)
{
	if (a.l == b.l) return a.r > b.r;
	return a.l < b.l;
}

int main()
{
	scanf("%d%d", &n, &L);
	for (int i = 1; i <= n; i ++ )
	{
		scanf("%d%d", &a[i].l, &a[i].r);
	}
	sort(a + 1, a + 1 + n, cmp);
	int ans = solve();
	printf("%d", ans);
	return 0;
}