#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pi = pair<pair<int, int>, pair<int, int>>;
#define ff first
#define ss second
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define lb lower_bound
#define int ll
int N, M, ST[800005], lazy[800005], L[200005], R[200005];
void prop(int v, int l, int r) {
if(l == r) return;
lazy[v * 2] += lazy[v];
lazy[v * 2 + 1] += lazy[v];
ST[v * 2] += lazy[v];
ST[v * 2 + 1] += lazy[v];
lazy[v] = 0; return;
}
void update(int v, int l, int r, int lo, int hi, int val) {
prop(v, l, r);
if(l > hi || r < lo) return;
if(l >= lo && r <= hi) {
ST[v] += val; lazy[v] += val;
return;
}
update(v * 2, l, (l + r) / 2, lo, hi, val);
update(v * 2 + 1, (l + r) / 2 + 1, r, lo, hi, val);
ST[v] = min(ST[v * 2], ST[v * 2 + 1]);
}
int query(int v, int l, int r, int lo, int hi) {
prop(v, l, r);
if(l > hi || r < lo) return 1e9 + 7;
if(l >= lo && r <= hi) return ST[v];
return min(query(v * 2, l, (l + r) / 2, lo, hi),
query(v * 2 + 1, (l + r) / 2 + 1, r, lo, hi));
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> N >> M;
for(int l = 1; l <= N; l++) L[l] = l, R[l] = l;
for(int l = 1; l <= M; l++) {
int U, V; cin >> U >> V;
L[V] = min(L[V], U); L[U] = min(L[U], V);
R[V] = max(R[V], U); R[U] = max(R[U], V);
}
int i = 1;
for(int l = 2; l <= N; l++) {
while(i < l && R[i] <= l) i++;
update(1, 1, N, 1, L[l] - 1, 1);
int P = query(1, 1, N, 1, i - 1);
update(1, 1, N, l, l, P);
}
cout << ST[1] << "\n";
return 0;
}
