#include <bits/stdc++.h>

using namespace std;

const int N = 2e5 + 5, INF = 0x3f3f3f3f;

int n, m;
int g[N], mn[N];
int f[N], cnt[N];

struct Node{
    int a, b;
    int v, t;
}t[N * 4];

#define ls (u << 1)
#define rs (u << 1 | 1)
inline void PushUp(int u)
{
    t[u].v = min(t[ls].v, t[rs].v);
}
inline void Change(int u, int d)
{
    t[u].v += d, t[u].t += d;
}
inline void PushDown(int u)
{
    if(t[u].t)
    {
        Change(ls, t[u].t);
        Change(rs, t[u].t);
        t[u].t = 0;
    }
}
inline void Build(int u, int a, int b)
{
    t[u].a = a, t[u].b = b;
    if(a != b)
    {
        int mid = (a + b) >> 1;
        Build(ls, a, mid);
        Build(rs, mid + 1, b);
    }
}
inline void Modify(int u, int x, int y, int d)
{
    if(x <= t[u].a && t[u].b <= y) return Change(u, d);
    PushDown(u);
    if(t[ls].b >= x) Modify(ls, x, y, d);
    if(t[rs].a <= y) Modify(rs, x, y, d);
    PushUp(u);
}
inline int Query(int u, int x, int y)
{
    if(x <= t[u].a && t[u].b <= y) return t[u].v;
    PushDown(u);
    int res = INF;
    if(t[ls].b >= x) res = min(res, Query(ls, x, y));
    if(t[rs].a <= y) res = min(res, Query(rs, x, y));
    return res;
}

int main()
{
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i ++ ) g[i] = i;
    for(int i = 1; i <= m; i ++ )
    {
        int a, b;
        scanf("%d%d", &a, &b);
        g[a] = min(g[a], b);
        g[b] = min(g[b], a);
    }
    mn[n + 1] = n + 1;
    for(int i = n; i >= 1; i -- ) mn[i] = min(mn[i + 1], g[i]);
    Build(1, 1, n);
    for(int i = 2; i <= n; i ++ )
    {
        if(g[i] > 1) Modify(1, 1, g[i] - 1, 1);
        if(mn[i + 1] == 1)
        {
            f[i] = INF;
            Modify(1, i, i, INF);
            continue;
        }
        f[i] = Query(1, 1, min(i - 1, mn[i + 1] - 1));
        Modify(1, i, i, f[i]);
    }
    printf("%d\n", f[n]);
    return 0;
}