#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
int solve(ll a) {
  int m = 0;
  while(a > 0) {
  ll l = a&-a;
    ll b=a&~(a+l);
m=max(m,__builtin_popcountll(b));
a^=b;
  }
return m;
}
int main(){
ll b = 0;
int d;cin>>d;
rep(i,2) {
 string s;cin>>s;
 rep(j, 7) {
  b |= s[j] == 'o' ? 1 << (i * 7 + j) : 0;
 }
}
b <<= 14;
int m=0;
rep(i, 29){
rep(j,d+1) {
ll q=((1LL<<j)-1LL)<<i;
if(b&q)continue;
m=max(m, solve(b | q));
}
}
cout<<m<<endl;
}