#include <bits/stdc++.h>
using namespace std;

#define endl        '\n'
#define pb push_back
const int MAXN    = 2e5+9;
/*-----------------------------------------------------------------------------------------------------*/

int pa[MAXN], sz[MAXN];
int fnd(int x) {return(x==pa[x]?x:pa[x]=fnd(pa[x]));}
bool uni(int a, int b) {
    if((a=fnd(a))==(b=fnd(b))) return false;
    if(sz[a]>sz[b]) swap(a, b);
    pa[a]=b; sz[b]+=sz[a];
    return true;
}
//O(mlogn+nlogn)
int main() {
    ios::sync_with_stdio(0); cin.tie(NULL);

    for(int i = 0; i < MAXN; i++) pa[i]=i, sz[i]=1;
    int n, m, a, b, ans=0, nm=0, cur;
    cin >> n >> m;
    vector<int> edge[MAXN];
    for(int i = 0; i <m; i++) {
        cin >> a >> b;
        if(a>b) swap(a, b);
        edge[a].pb(b);
        uni(a, b);
    }//O(mlogn)

    for(int i = 1; i <= n; i++) {
        cur=0;
        for(int x: edge[i]) {
            cur=max(cur, x);
        }//O(n+m)
        if(cur==0) continue;
        for(int j = cur; j> max(nm, i); j--) {
            if(uni(i, j)) {
                ans++;
            }
        }//O(n+nlogn)
        if((nm=cur)==n) break;
    }
    cout << ans <<endl;

	return 0;
}