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

#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define intll int long long
const int INF = 1e9;
const int MOD = 1e9 + 7;

int main() {
  int n ; 
  cin >> n ;
  string s , t  ;
  cin >> s >> t ;
  deque<char> S , T ;
  rep(i,n){
    S.push_back(s.at(i)) ;
    T.push_back(t.at(i));
  }
  if(s == t ) {
    cout << s.size() <<endl ; 
    return 0 ;
  }
  
  int ans = 2 * n ;
  
  rep(i,n){
    S.pop_front();
    T.pop_back();
    
    if( S == T){
      ans = S.size() + 2*(i+1) ;
      cout <<  ans <<endl ;
      return 0 ;
    }
  }
    
  
}

// agc006_a
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <type_traits>
#include <typeindex>
#include <unordered_map>
#include <unordered_set>
#endif

template <typename A, typename B> bool cmin(A &a, const B &b) {
  return a > b ? (a = b, true) : false;
}
template <typename A, typename B> bool cmax(A &a, const B &b) {
  return a < b ? (a = b, true) : false;
}
const double PI = acos(-1);
const double EPS = 1e-9;
int inf = sizeof(int) == sizeof(long long) ? 2e18 : 1e9 + 10;
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
#define rep(i, n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main()
{
  int N, index=0;
  string S,T;
  cin>>N>>S>>T;
  rep (i, N) {
    if (S.substr(N-1-i) == T.substr(0, i+1)) {
      index = i+1;
    }
  }
  cout<<2*N-index<<endl;
  return 0;
}
