#include <iostream>
#include <vector>
using namespace std;
int main(){
  int d;
  cin>>d;
  char c;
  int a,b,m;
  a=0;
  b=0;
  m=0;
  vector<int> va;
  for(int i=0; i<7; ++i){
    cin>>c;
    if(c=='x'){
      b--;
      if(a!=0){
        va.push_back(a);
        a=0;
      }
    } else {
      a++;
      if(b!=0) {
        va.push_back(b);
        b=0;
      }
    }
  }
  for(int i=0; i<7; ++i){
    cin>>c;
    if(c=='x'){
      b--;
      if(a!=0){
        va.push_back(a);
        a=0;
      }
    } else {
      a++;
      if(b!=0) {
        va.push_back(b);
        b=0;
      }
    }
  }

  if(a!=0){
    va.push_back(a);
    a=0;
  } else if(b!=0) {
    va.push_back(b);
    b=0;
  }

  for(int i=0; i<va.size(); ++i){
    vector<int> vb;
    vb=va;
    int x;
    x=0;
    if(vb[i]<0){
      if(vb[i]*-1<=d){
        x=vb[i]*-1;
        if(i>0 && i<va.size()-1){
          x+=vb[i-1];
          x+=vb[i+1];
          if(x>m){
            m=x;
          }
        } else if(i==0){
          x+=vb[i+1];
          if(x>m){
            m=x;
          }
        } else{
          x+=vb[i-1];
          if(x>m){
            m=x;
          }
        }
      } else {
        x=d;
        if(i>0 && i<va.size()-1){
          if(vb[i-1]>=vb[i+1]) x+=vb[i-1];
          else x+=vb[i+1];
          if(x>m){
            m=x;
          }
        } else if(i==0){
          x+=vb[i+1];
          if(x>m){
            m=x;
          }
        } else{
          x+=vb[i-1];
          if(x>m){
            m=x;
          }
        }
      }
    }
  }
  int ml,mr;
  ml=va[0]+d;
  if(ml>m) m=ml;
  mr=va[va.size()-1]+d;
  if(mr>m) m=mr;

  cout<<m<<endl;
  return 0;
}