#include <iostream>
#include <cstdio>
#define lpos pos << 1
#define rpos pos << 1 | 1
using namespace std;

const int MAXN = 1e4 + 5;

int l, m, u, v;

struct tree
{
	int l, r, val, tag;
}t[MAXN << 2];

inline void pushdown(int pos)
{
	if (t[pos].tag)
	{
		t[lpos].val = t[rpos].val = t[pos].tag;
		t[lpos].tag = t[rpos].tag = t[pos].tag;
		t[pos].tag = 0;
	}
}

inline void build(int pos, int l, int r)
{
	t[pos].l = l, t[pos].r = r;
	if (l == r)
	{
		t[pos].val = 1;
		return;
	}
	int mid = (l + r) >> 1;
	build(lpos, l, mid);
	build(rpos, mid + 1, r);
	t[pos].val = t[lpos].val + t[rpos].val;
}

inline void update(int pos, int L, int R)
{
	int l = t[pos].l, r = t[pos].r;
	if (l >= L && r <= R)
	{
		t[pos].val = t[pos].tag = 0;
		return;
	}
	pushdown(pos);
	int mid = (l + r) >> 1;
	if (L <= mid)
	{
		update(lpos, L, R);
	}
	if (R > mid)
	{
		update(rpos, L, R);
	}
	t[pos].val = t[lpos].val + t[rpos].val;
}

int main()
{
	scanf("%d%d", &l, &m);
	l++;
	build(1, 1, l);
	while (m--)
	{
		scanf("%d%d", &u, &v);
		u++, v++;
		update(1, u, v);
	}
	printf("%d", t[1].val);
	return 0;
}