#include <bits/stdc++.h>
using namespace std;
int n, dp[200];
bool pr[200];
string s;
int main(){
	freopen("lepus.in", "r", stdin);
	freopen("lepus.out", "w", stdout);
	cin >> n >> s;
	dp[n-1] = -1;
	pr[0] = 1;
	for(int i = 0; i < n; i++){
		if(i == n-1){
			break;
		}
		if(s[i] != 'w' && pr[i] == 1){
			if(s[i] == '"'){
				dp[i] += 1;
			}
			dp[i + 1] = max(dp[i+1], dp[i]);
			pr[i+1] = 1;
			dp[i + 3] = max(dp[i+3], dp[i]);
			pr[i+3] = 1;
			dp[i + 5] = max(dp[i+5], dp[i]);
			pr[i+5] = 1;
		}
		else{
			dp[i] = -1;
		}
	}
	if(dp[n-1] == -1){
		cout << -1;
	}
	else{
		cout << dp[n-1];
	}
	return 0;
}
//3
//-1 2 1