#define re register int 
#define il inline
#define ll long long
using namespace std;
const int inf=1e9;
il int read(){
	char c=getchar();int z=0,f=1;
	while(c!='-'&&(c>'9'||c<'0')) c=getchar();
	if(c=='-') f=-1,c=getchar();
	while(c>='0'&&c<='9') z=(z<<1)+(z<<3)+c-'0',c=getchar();
	return z*f;
}
int R,n;
int mp[1100002],a[1100002];
int ans;
struct ANS{
	int x,y;
}q[1100002];
il void dfs(int l,int now,int r,int sum){
	if(r>=R) return ;
	if(mp[now]<l) return ;
	if(r==mp[now]&&sum>1&&sum==r-l+1) {
		q[++ans].x=l,q[ans].y=r,R=min(R,r);
		return ;
	}
	dfs(l,now+1,max(r,mp[now+1]),sum+1);
}
int main (){
	//Fuyuki是我们的红太阳 
	freopen("empodia.in","r",stdin);
	freopen("empodia.out","w",stdout);
	n=read();R=n+1;
	for(re i=1;i<=n;i++) a[i]=read(),mp[a[i]]=i;
	for(re i=n-2;i>=1;i--) 
		dfs(i,a[i],i,1);
	cout<<ans<<'\n';
	for(re i=ans;i>=1;i--)
		cout<<q[i].x<<' '<<q[i].y<<'\n';
	return 0;
}

#include <bits/stdc++.h>
#define re register int 
#define il inline
#define ll long long
using namespace std;
const int inf=1e9;
il int read(){
	char c=getchar();int z=0,f=1;
	while(c!='-'&&(c>'9'||c<'0')) c=getchar();
	if(c=='-') f=-1,c=getchar();
	while(c>='0'&&c<='9') z=(z<<1)+(z<<3)+c-'0',c=getchar();
	return z*f;
}
int R,n;
int mp[1100002],a[1100002];
int ans;
struct ANS{
	int x,y;
}q[1100002];
il void dfs(int l,int now,int r,int sum){
	if(r>=R) return ;
	if(mp[now]<l) return ;
	if(r==mp[now]&&sum>1&&sum==r-l+1) {
		q[++ans].x=l,q[ans].y=r,R=min(R,r);
		return ;
	}
	dfs(l,now+1,max(r,mp[now+1]),sum+1);
}
int main (){
	//Fuyuki是我们的红太阳 
	freopen("empodia.in","r",stdin);
	freopen("empodia.out","w",stdout);
	n=read();R=n+1;
	for(re i=1;i<=n;i++) a[i]=read(),mp[a[i]]=i;
	for(re i=n-2;i>=1;i--) 
		dfs(i,a[i],i,1);
	cout<<ans<<'\n';
	for(re i=ans;i>=1;i--)
		cout<<q[i].x<<' '<<q[i].y<<'\n';
	return 0;
}