#include<iostream>
#include<algorithm>
#include<climits>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<ctime>
#include<string>
#include<cstring>
#include<vector>
#include<stack>
#include<queue>
#include<set>
#include<bitset>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;

#define PI 3.141592653589793238462643383279
#define mod 1000000007LL
#define rep(i, n) for(i = 0;i < n;++i)
#define rep1(i, n) for(i = 1;i < n;++i)
#define per(i, n) for(i = n - 1;i > -1;--i)
#define int(x) int x; scanf("%d",&x)
#define int2(x, y) int x, y; scanf("%d%d",&x, &y)
#define int3(x, y, z) int x, y, z; scanf("%d%d%d",&x, &y, &z)
#define int4(v, x, y, z) int v, x, y, z; scanf("%d%d%d%d", &v, &x, &y, &z)
#define int5(v, w, x, y, z) int v, w, x, y, z; scanf("%d%d%d%d%d", &v, &w, &x, &y, &z)
#define ll2(x, y) ll x, y; cin >> x >> y;
#define scn(n, a) rep(i, n)cin >> a[i]
#define sc2n(n, a, b) rep(i, n)cin >> a[i] >> b[i]
#define pri(x) cout << (x) << "\n"
#define pri2(x, y) cout << (x) << " " << (y) << "\n"
#define pri3(x, y, z) cout << (x) << " " << (y) << " " << (z) << "\n"
#define pb push_back
#define mp make_pair
#define all(a) (a).begin(),(a).end()
#define endl "\n"
#define kabe puts("---------------------------")
#define kara puts("")
#define debug(x) cout << " --- " << (x) << "\n"
#define debug2(x, y) cout << " --- " << (x) << " " << (y) << "\n"
#define debug3(x, y, z) cout << " --- " << (x) << " " << (y) << " " << (z) << "\n"
#define X first
#define Y second
#define eps 0.0001
#define prid(x) printf("%.15lf\n", x)

struct edge{
  int to, cost;
};
vector<edge> G[250];
int x[250], y[250];

ll bellmanford(int ma){
  int v = ma + ma;
  int n = ma - 2;
  ll d[v], res = 0, longinf = 123451234512345LL;
  int roopcnt, i, j;
  rep(i, v)d[i] = longinf;
  d[0] = 0LL; d[ma] = 0LL;
  for(roopcnt = 0;roopcnt < v;roopcnt++){
    bool upd = false;
    rep(i, v){
      rep(j, G[i].size()){
        edge tmp = G[i][j];
        if(d[i] != longinf && d[tmp.to] > d[i] + tmp.cost){
          d[tmp.to] = d[i] + tmp.cost;
          upd = true;
        }
      }
    }
    if(!upd)break;
  }
  res = longinf;
  if(x[n - 1] != 2)res = min(res, d[n - 1]);
  res = min(res, d[n]);
  res = min(res, d[n + 1]);
  if(y[n - 1] != 2)res = min(res, d[ma + n - 1]);
  res = min(res, d[ma + n]);
  res = min(res, d[ma + n + 1]);
  if(res == longinf)pri("NA");
  else pri(res);
  //rep(i, ma + ma)pri2(i, d[i]);
  return res;
}

signed main(void){
  int i, j;
  for(int testcase = 0;testcase >= 0;testcase++){
    int(n);
    if(!n)break;

    int ma = n + 2;
    rep(i, 250)x[i] = 0;
    rep(i, 250)y[i] = 0;
    scn(n, x);
    scn(n, y);
    rep(i, n){
      if(x[i] == 0){
        G[i].pb((edge){ma + i, 1});
        G[i].pb((edge){ma + i + 1, 1});
        G[i].pb((edge){ma + i + 2, 1});
      }else if(x[i] == 1){
        if(x[i + 1] == 1)G[i].pb((edge){i + 1, 0});
        else{
          G[i].pb((edge){ma + i, 1});
          G[i].pb((edge){ma + i + 1, 1});
          G[i].pb((edge){ma + i + 2, 1});
        }
      }else{
        G[i].pb((edge){i - 1, 0});
      }
    }
    rep(i, n){
      if(y[i] == 0){
        G[ma + i].pb((edge){i, 1});
        G[ma + i].pb((edge){i + 1, 1});
        G[ma + i].pb((edge){i + 2, 1});
      }else if(y[i] == 1){
        if(y[i + 1] == 1)G[ma + i].pb((edge){ma + i + 1, 0});
        else{
          G[ma + i].pb((edge){i, 1});
          G[ma + i].pb((edge){i + 1, 1});
          G[ma + i].pb((edge){i + 2, 1});
        }
      }else{
        G[ma + i].pb((edge){ma + i - 1, 0});
      }
    }

    bellmanford(ma);
    rep(i, 250)G[i].clear();

//*/

//*/ break;
  }
  return 0;
}

Measured memory_bytes: 3200