#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
struct SegTree{
	int size;
	vector<pii>arr;
	void init(int n){
		size = 1;
		while(size<n)size*=2;
		arr.resize(2*size);
	}
	void set(int i, pii v, int x, int lx, int rx){
		if(rx-lx==1){
			arr[x] = v;
			return;
		}
		int m = (lx+rx)/2;
		if(i<m){
			set(i,v,2*x+1,lx,m);
		}
		else{
			set(i,v,2*x+2,m,rx);
		}
		arr[x] = min(arr[2*x+1],arr[2*x+2]);
	}
	void set(int i,pii v){
		set(i,v,0,0,size);
	}
	pii query(int l,int r, int x, int lx, int rx){
		if(lx>=r||l>=rx)return {(int)1e9+7,0LL};
		if(lx>=l&&rx<=r)return arr[x];
		int m = (lx+rx)/2;
		pii s1 = query(l,r,2*x+1,lx,m);
		pii s2 = query(l,r,2*x+2,m,rx);
		return min(s1,s2);
	}
	pii query(int l, int r){
		return query(l,r,0,0,size);
	}
};
struct SegTree2{
	int size;
	vector<pii>arr;
	void init(int n){
		size = 1;
		while(size<n)size*=2;
		arr.resize(2*size);
	}
	void set(int i, pii v, int x, int lx, int rx){
		if(rx-lx==1){
			arr[x] = v;
			return;
		}
		int m = (lx+rx)/2;
		if(i<m){
			set(i,v,2*x+1,lx,m);
		}
		else{
			set(i,v,2*x+2,m,rx);
		}
		arr[x] = max(arr[2*x+1],arr[2*x+2]);
	}
	void set(int i,pii v){
		set(i,v,0,0,size);
	}
	pii query(int l,int r, int x, int lx, int rx){
		if(lx>=r||l>=rx)return {0LL,0LL};
		if(lx>=l&&rx<=r)return arr[x];
		int m = (lx+rx)/2;
		pii s1 = query(l,r,2*x+1,lx,m);
		pii s2 = query(l,r,2*x+2,m,rx);
		return max(s1,s2);
	}
	pii query(int l, int r){
		return query(l,r,0,0,size);
	}
};
signed main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	int n;
	cin >> n;
	vector<int>l(n+1);
	vector<int>r(n+1);
	vector<int>sorted;
	for(int i = 1; i<=n; i++){
		cin >> l[i] >> r[i];
		sorted.push_back(l[i]);
		sorted.push_back(r[i]);
	}
	sorted.push_back(-69);
	sort(sorted.begin(),sorted.end());
	for(int i = 1; i<=n; i++){
		l[i] = lower_bound(sorted.begin(),sorted.end(),l[i])-sorted.begin();
		r[i] = lower_bound(sorted.begin(),sorted.end(),r[i])-sorted.begin();
	}
	SegTree left;
	SegTree2 right;
	left.init(2*n+5);
	right.init(2*n+5);
	vector<pii>lt(2*n+1,{(int)1e9,(int)1e9});
	vector<pii>rt(2*n+1);
	vector<vector<int>>lts(2*n+1);
	vector<vector<int>>rts(2*n+1);
	for(int i = 1; i<=n; i++){
		lt[r[i]] = min(lt[r[i]],{l[i],i});
		rt[l[i]] = max(rt[l[i]],{r[i],i});
		lts[r[i]].push_back(l[i]);
		rts[l[i]].push_back(r[i]);
	}
	for(int i = 1; i<=2*n; i++){
		right.set(i,rt[i]);
		left.set(i,lt[i]);
	}
	vector<int>dpl(2*n+5);
	vector<int>dpr(2*n+5);
	{
		int far = 0;
		for(int i = 1; i<=2*n; i++){
			if(lt[i] == make_pair((int)1e9,(int)1e9)){
				dpl[i] = dpl[i-1];
				continue;
			}
			else{
				for(int nxt: lts[i]){
					far = max(far,nxt);
				}
			}
			auto p = left.query(far,i+1);
			dpl[i] = dpl[p.first-1]+1;
		}
	}
	{
		int far = 2*n+1;
		for(int i = 2*n; i>=1; i--){
			if(rt[i] == make_pair(0,0)){
				dpr[i] = dpr[i+1];
				continue;
			}
			else{
				for(int nxt: rts[i]){
					far = min(far,nxt);
				}
			}
			auto p = right.query(i,far+1);
			dpr[i] = dpr[p.first+1]+1;
		}
	}
	int best = dpl[2*n];
	const int ln = 24;
	vector<vector<int>>dp(n+1,vector<int>(ln));
	for(int i = 1; i<=n; i++){
		auto p = right.query(l[i],r[i]+1);
		dp[i][0] = p.second;
	}
	for(int j = 1; j<ln; j++){
		for(int i = 1; i<=n; i++){
			dp[i][j] = dp[dp[i][j-1]][j-1];
		}
	}
	// cout << '\n';
	// for(int i = 1; i<=n; i++){
	// 	cout << l[i] << ' ' << r[i] << '\n';
	// }
	// for(int i = 1; i<=2*n; i++){
	// 	cout << dpl[i] << ' ' ;
	// }
	// cout << '\n';
	// for(int i = 1; i<=2*n; i++){
	// 	cout << dpr[i] << ' ' ;
	// }
	// cout << '\n';
	int ans = (int)1e9;
	for(int i = 1; i<=n; i++){
		int ret = 0;
		int u = i;
		for(int j = ln-1; j>=0; j--){
			int nu = dp[u][j];
			if(1 + dpl[l[i]-1] + dpr[r[nu]+1] < best){
				continue;
			}
			u = nu;
			ret+=1<<j;
		}
		if(ret < (1<<22)){
			ans = min(ans,ret+1);
		}
	}
	if(ans==(int)1e9){
		cout << "impossible\n";
		return 0;
	}
	cout << ans << '\n';
	return 0;
}