#include<iostream>#include<cstring>#include<vector>#include<algorithm>using namespace std;int mainw(int n){ int data[10000],a[10000],c[10000],i,j,k; vector<int> ans; memset(a,0,sizeof(a)); memset(c,0,sizeof(c)); for(i=1;i<=n;i++) cin>>data[i]; for(i=2;i<=n;i++) for(j=i-1;j>0;j--) if(data[i] == data[j]){ if(a[j] == 0) a[j] = i; c[i] = j; break; } for(i=1;i<=n;){ j = i + 1; while(c[j] == 0 && j <= n) ++j; if(j > n) break; else if(a[j] != 0){ c[a[j]] = 0; } k = j + 1; while(c[k] == 0 && k <= n) ++k; if(k > n) break; else if(a[k] != 0){ c[a[k]] = 0; } ans.push_back(c[j]); ans.push_back(j); ans.push_back(c[k]); ans.push_back(k); for(;i<=k;++i){ c[a[i]] = 0; } } cout<<ans.size()/4<<endl; sort(ans.begin(),ans.end()); for(i=0;i<ans.size();i++){ cout<<ans[i]; if((i+1)%4) cout<<' '; else cout<<endl; }}int main(){ int n; bool flag = false; while(cin>>n){ if(flag) cout<<endl; mainw(n); flag = true; } return 0;}
