#include <stdio.h>
#include <string.h>

int main(void){
	int i,d;
	int okMax = 0;
	
	char s[10];
	char week[30];
	
	scanf("%d", &d);
	
	scanf("%s", s);
	for(i=0;i<7;i++){
		week[i] = s[i];
	}
	
	scanf("%s", s);
	for(;i<15;i++){
		week[i] = s[i-7];
	}
	
	for(i=0;i<(14-d+1);i++){
		int ok=0;
		int j,rest = d;
		char tmp[30];
		strcpy(tmp, week);
		
		for(j=0;j<rest;j++){
			if(14 <= i+j){break;}
			tmp[i+j] = 'o';
		}
		for(j=0;j<15;j++){
			if(tmp[j] == 'o'){
				ok++;
			}else{
				if(okMax < ok ){
					okMax = ok;
				}
				ok = 0;
			}
		}
	}
	
	printf("%d\n", okMax);
	
	return 0;
}