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

typedef pair<int, int> ii;
typedef pair<char, int> ci;

mt19937 rng(time(0));

vector<string> a;

struct cmp{
    long long operator()(const ii aa) const{
        return (1LL*aa.first<<32) + aa.second;
    }
    long long operator()(const ci aa) const{
        return (1LL*aa.second<<32) + aa.first;
    }
};

int nope(int ret){
   return ret^((1<<5)-1);
}
unordered_set<ii, cmp> ans;
vector<vector<int>> indices;
unordered_map<ci, int, cmp> hashed;
long long mx = 1e18;

void solve(){
   ci par;
   int idx = 0;
   hashed.clear();
   for(const auto & x : a){
       int ret = 0;
       if((int)ans.size() >= mx) return;
       for(int j = 0; j < 5; j++){
           par = {x[j], j};
           if(hashed.count(par) == 0){
               hashed[par] = rng()%2;
           }
           ret|=(hashed[par]<<j);
       }
       indices[ret].push_back(++idx);
   }

   for(int i = 0 ; i < (1<<5); i++){
       for(const auto &j : indices[i]){
           for(int ret = indices[nope(i)].size()-1; ret >=0; ret--){
               int jj = indices[nope(i)][ret];
               if((int)ans.size() >= mx) return;
               ans.insert({j < jj ? j : jj, j < jj ? jj : j});
           }
       }
       indices[i].clear();
       indices[nope(i)].clear();
   }
}

int main(){
    cout.tie(NULL), cin.tie(NULL);
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;
    indices.resize(1<<5);
    a.resize(n);
    mx = min(100000*1LL, 1LL*n*(n+1)/2);
    for(int i = 0; i < n; i++){
        cin >> a[i];
    }

    for(int i = 0; i < 600 && (int)ans.size() < mx; i++){
        solve();
    }

    auto it = ans.begin();
    printf("%lld\n", min((long long)ans.size(), mx));
    for(int i = 0; i < (int)ans.size() && i < mx; i++){
        printf("%d %d\n", it->second, it->first);
        ++it;
    }

    return 0;
}