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太久沒寫模擬，總是寫一般覺得紕漏太多

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <iomanip>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <vector> 
//
 
 #include <bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define sp ' '
#define endl '\n'
#define inf  0x3f3f3f3f;
#define FOR(i,a,b) for( int i = a;i <= b;++i)
#define bug cout<<"--------------"<<endl
#define P pair<int, int>
#define fi first
#define
 
 se second
#define pb(x) push_back(x)
#define ppb() pop_back()
#define mp(a,b) make_pair(a,b)
#define ms(v,x) memset(v,x,sizeof(v))
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repd(i,a,b) for(int i=a;i>=b;i--)
#define sca3(a,b,c) scanf("%d %d %d",&(a),&(b),&(c))
#define sca2(a,b) scanf("%d %d",&(a),&(b))
#define
 
 sca(a) scanf("%d",&(a));
#define sca3ll(a,b,c) scanf("%lld %lld %lld",&(a),&(b),&(c))
#define sca2ll(a,b) scanf("%lld %lld",&(a),&(b))
#define scall(a) scanf("%lld",&(a));


using namespace std;
typedef long long ll;
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll powmod(ll a, ll b, ll mod){ll sum = 1;while (b) {if (b & 1) {sum = (sum * a) % mod;b--;}b /= 2;a = a * a % mod;}return sum;}

const double Pi = acos(-1.0);
const double epsilon = Pi/180.0;
const int maxn = 150000+ 100; 
vector<int>v1[30],v2[30];
int vis1[maxn],vis2[maxn];
char a[maxn],b[maxn];
int main()
{
    int n;
    cin>>n;
    queue<int>que1,que2;
    rep(i,1,n){
        char c;
        cin>>c;
        a[i] = c;
        if(c-'a' == -34) {
            que1.push(i);
            continue;
        }
        v1[c-'a'].pb(i);
    }
    rep(i,1,n){
        char c;
        cin>>c;
        b[i] = c;
        if(c-'a' == -34) {
            que2.push(i);
            continue;
        }
        v2[c-'a'].pb(i);
    }
    queue<pair<int,int> > ans;
    rep(i,0,25){
        int minn = min(v1[i].size(),v2[i].size());
        for(int j = 0; j < minn;++j){
/*            vis1[v1[i][j]] = 1;
            vis2[v2[i][j]] = 1;*/
            ans.push(mp(v1[i][j],v2[i][j]));
        }
        if(v2[i].size() > v1[i].size()){
            while(1){
                if(minn == v2[i].size() || que1.size() ==0){
                    break;
                }
                int tmp = que1.front();que1.pop();
                ans.push(mp(tmp,v2[i][minn]));
                minn++;
            }
        }
        else {
             while(1){
                if(minn == v1[i].size() || que2.size() ==0){
                    break;
                }
                int tmp = que2.front();que2.pop();
                ans.push(mp(v1[i][minn],tmp));
                minn++;
            }           
        }
    }
    while(1){
        if(que1.size() == 0 || que2.size() == 0) break;
        int x = que1.front();que1.pop();
        int y = que2.front();que2.pop();
        ans.push(mp(x,y));
    }

    cout<<ans.size()<<endl;
    while(ans.size()){
        int x = ans.front().fi;
        int y = ans.front().se;
        ans.pop();
        cout<<x<<sp<<y<<endl;
    }



}