#include <stdio.h>

void chmax(int* a, int b)
{
	if (*a < b) *a = b;
}

int count(char S[])
{
	int i, j, k, l, dp[2][501][501], q[2][250001][2], head, tail, cur, prev, tmp;
	for (l = 0; S[l] != 0; l++);
	for (i = 0; i <= l; i++) {
		for (j = 0; j <= l; j++) {
			dp[0][i][j] = -1;
			dp[1][i][j] = -1;
		}
	}
	dp[1][0][0] = 0;
	q[1][0][0] = 0;
	q[1][0][1] = 0;
	tail = 1;
	for (k = 0, cur = 0, prev = 1; k < l; k++, cur ^= 1, prev ^= 1) {
		for (head = tail - 1, tail = 0; head >= 0; head--) {
			i = q[prev][head][0];
			j = q[prev][head][1];
			tmp = dp[prev][i][j];
			dp[prev][i][j] = -1;
			
			if (dp[cur][i][j] == -1) {
				q[cur][tail][0] = i;
				q[cur][tail++][1] = j;
			}
			chmax(&(dp[cur][i][j]), tmp);
			
			if (S[k] == 'p') {
				if (j == 0) {
					if (dp[cur][i+1][j] == -1) {
						q[cur][tail][0] = i + 1;
						q[cur][tail++][1] = j;
					}
					chmax(&(dp[cur][i+1][j]), tmp);
				} else if (j % 2 == 0) {
					if (dp[cur][i][j+1] == -1) {
						q[cur][tail][0] = i;
						q[cur][tail++][1] = j + 1;
					}
					chmax(&(dp[cur][i][j+1]), tmp);
				}
			} else if (S[k] == 'o') {
				if (i > 0 && j == 0) {
					if (dp[cur][i-1][j+2] == -1) {
						q[cur][tail][0] = i - 1;
						q[cur][tail++][1] = j + 2;
					}
					chmax(&(dp[cur][i-1][j+2]), tmp);
				} else if (j % 2 != 0) {
					if (dp[cur][i][j+1] == -1) {
						q[cur][tail][0] = i;
						q[cur][tail++][1] = j + 1;
					}
					chmax(&(dp[cur][i][j+1]), tmp);
				}
			} else {
				if (j > 0 && j % 2 == 0) {
					if (dp[cur][i][j-2] == -1) {
						q[cur][tail][0] = i;
						q[cur][tail++][1] = j - 2;
					}
					chmax(&(dp[cur][i][j-2]), tmp + 1);
				}
			}
		}
	}
	
	int ans = 0;
	for (head = 0; head < tail; head++) {
		i = q[prev][head][0];
		j = q[prev][head][1];
		chmax(&ans, dp[prev][i][j]);
	}
	return ans;
}

int main()
{
	int N;
	char S[501];
	scanf("%d", &N);
	scanf("%s", S);
	
	int i, j, k, ans = -1;
	char c;
	for (i = 3; i < N - 2; i++) {
		c = S[i];
		S[i] = 0;
		j = count(S);
		S[i] = c;
		k = count(&(S[i]));
		if (j >= 1 && k >= 1) chmax(&ans, j + k - 2);
	}
	printf("%d\n", ans);
	fflush(stdout);
	return 0;
}