#include <cstring>
#include <algorithm>
#include <cstdio>
#include <iostream>
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
/* ここからが本編 */
/* */
int main(void)
{
  int i;
  int d;
  char s[17];
  char tmp[10];
  int start,end;
  int o1,o2,x1;
  int max = 0;
  int mem1 = 0;
  cin >> d;
  cin >> s;
  cin >> tmp;
  strcat(s,tmp);

 part1:
  for(i=0;i<14;) {
	for(i=mem1;;i++) {
	  if(s[i] == 'o') {
		start = i; break;
	  }
	  if(s[i] == 0) goto part2;
	}
	for(; ;i++) {
	  if(s[i] != 'o') {
		end = i-1; break;
	  }
	}
	// printf("part1_o1_end = %d\n",end);
	o1 = end - start + 1;
  
	for(; ;i++) {
	  if(s[i] == 'x') {
		start = i; break;
	  }
	  if(s[i] == 0) goto part2;
	}
	for(;i<14;i++) {
	  if(s[i] != 'x') {
		end = i-1; break;
	  }
	}
	// printf("part1_x1_end = %d\n",end);
	// s[i] = 'o' or 0
	mem1 = i;
	x1 = end - start + 1;
	// printf("part1_x1 = %d\n",x1);
	for(; ;i++) {
	  if(s[i] == 'o') {
		start = i; break;
	  }
	  if(s[i] == 0) goto part2;
	}
	for(;;i++) {
	  if(s[i] != 'o') {
		end = i-1; break;
	  }
	}
	o2 = end - start + 1;
	if(x1 > d) {
	  if(max < o1+d) max = o1+d;
	  if(max < o2+d) max = o2+d;

	  i--;
	  continue;
	}
	// printf("part1_o2_end = %d\n",end);
	if(max < o1+x1+o2) max = o1+x1+o2;
  }
 part2:
  
  for(i=0;;i++) {
	if(s[i] == 'o') {
	  start = i; break;
	}
	if(s[i] == 0) goto part3;
  }
  for(; ;i++) {
	if(s[i] != 'o') {
	  end = i-1; break;
	}
  }
  o1 = end - start + 1;
  if(max < o1+d) max = o1+d;

 part3:
  
  for(i=13;;i--) {
	if(s[i] == 'o') {
	  end = i; break;
	}
	if(i == 0) goto part4;
  }
  for(; i>=0;i--) {
	if(s[i] != 'o') {
	  start = i+1; break;
	}
  }
  o1 = end - start + 1;
  if(i < 0) goto part4;
  if(max < o1+d) max = o1+d;

 part4:
  if(max < d) max = d;
  printf("%d\n",max);
  return 0;
}