#include <stdio.h>

int note[16];

int main(void) {
	int d;
	char c[15];
	scanf("%d%s%s", &d, c, &c[7]);
	c[14] = 'x';
	
	int kinou = 'x', cnt = 0;
	note[0] = 15;
	int i;
	for(i = 0; i < 15; i++) {
		if(kinou != c[i]) {
			cnt++;
		}
		note[cnt]++;
		kinou = c[i];
	}
	note[cnt] += 15;
	
	int max = d;
	for(i = 1; i <= cnt - 1; i += 2) { // ここミスってた...
		int len;
		len = note[i] + ( (note[i - 1] <= d) ? (note[i - 1] + note[i - 2]) : d );
		if(max < len) { max = len; }
		len = note[i] + ( (note[i + 1] <= d) ? (note[i + 1] + note[i + 2]) : d );
		if(max < len) { max = len; }
	}
	printf("%d\n", max);
	return 0;
}