#include<bits/stdc++.h>
#define Yukinoshita namespace
#define Yukino std
using Yukinoshita Yukino;
int read()
{
	int s=0;
	char ch=getchar();
	while(ch<'0'||ch>'9') ch=getchar();
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s;
}
using vec=vector<int>;
stack<vec> A,C,AB,CB;
stack<vec> ABC,ACB,ABCB;
//CBAB A
//CBA AB
vec get(stack<vec> &a)
{
	vec res=a.top();
	a.pop();
	return res;
}
vec operator +(vec x,vec y)
{
	for(auto i:y) x.push_back(i);
	return x;
}
const int mxn=6e6+5;
char s[mxn];
/*
CABBCA

6
3 1 2 2 3 1

6
1 2 3 2 1 3
*/
int main()
{
	int n=read(),i;
	for(i=0;i<n;i++)
	{
		int x=s[i]=read()+'A'-1;
		if(x=='A')
		{
			if(CB.size())
				ABC.push(get(CB)+vec{i});
			else if(ACB.size())
			{
				vec tp=get(ACB);
				if(s[tp[0]]==x)
					ABC.push({tp[1],tp[2],i}),
					A.push({tp[0]});
				else
					ABC.push({tp[0],tp[2],i}),
					A.push({tp[1]});
			}
			else if(ABCB.size())
			{
				vec tp=get(ABCB);
				if(s[tp[0]]==x)
					AB.push({tp[0],tp[1]}),
					ABC.push({tp[2],tp[3],i});
				else
					AB.push({tp[2],tp[3]}),
					ABC.push({tp[0],tp[1],i});
			}
			else A.push({i});
		}
		if(x=='B')
		{
			if(A.size()&&C.size())
			{
				vec ta=get(A),tb=get(C);
				ACB.push({min(ta[0],tb[0]),max(ta[0],tb[0]),i}); 
			} 
			else if(A.size())
				AB.push(get(A)+vec{i});
			else if(C.size())
				CB.push(get(C)+vec{i});
			else if(ACB.size())
			{
				vec tp=get(ACB);
				if(s[tp[0]]=='A')
					AB.push({tp[0],i}),
					CB.push({tp[1],tp[2]});
				else
					CB.push({tp[0],i}),
					AB.push({tp[1],tp[2]});
			}
			else if(ABC.size())
				ABCB.push(get(ABC)+vec{i});
		}
		if(x=='C')
		{
			if(AB.size())
				ABC.push(get(AB)+vec{i});
			else if(ACB.size())
			{
				vec tp=get(ACB);
				if(s[tp[0]]==x)
					ABC.push({tp[1],tp[2],i}),
					C.push({tp[0]});
				else
					ABC.push({tp[0],tp[2],i}),
					C.push({tp[1]});
			}
			else if(ABCB.size())
			{
				vec tp=get(ABCB);
				if(s[tp[0]]==x)
					CB.push({tp[0],tp[1]}),
					ABC.push({tp[2],tp[3],i});
				else
					CB.push({tp[2],tp[3]}),
					ABC.push({tp[0],tp[1],i});
			}
			else C.push({i});
		}
	}
	printf("%d\n",ABC.size()+ABCB.size());
	for(;ABC.size();ABC.pop())
		printf("%d %d %d\n",ABC.top()[0],ABC.top()[1],ABC.top()[2]);
	for(;ABCB.size();ABCB.pop())
		printf("%d %d %d\n",ABCB.top()[0],ABCB.top()[1],ABCB.top()[2]);
}