#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pi = array<int, 2>;
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define fi first
#define se second
using ll = long long;
using pll = pair<ll, ll>;

int N, ans = -1;
char S[1010];

int main() {
	int d = 0;
	scanf("%d", &N);
	for (int i = 1; i <= N; i++) {
		scanf("%s", S);
		int a = 0, b = 0, t = 0;
		for (t = 0; S[t]; t++) {
			if (S[t] == 's')
				b++;
			if (S[t] == 't')
				a++;
		}
		if (S[t - 1] == '}')
			d--;
		if (d <= a) {
			if (b || d < a) {
				puts("-1");
				return 0;
			}
		} else {
			if (b % (d - a) != 0) {
				puts("-1");
				return 0;
			}
			if (ans != -1 && ans != b / (d - a)) {
				puts("-1");
				return 0;
			}
			ans = b / (d - a);
		}
		if (S[t - 1] == '{')
			d++;
	}
	if (ans == -1)
		puts("1");
	else
		printf("%d\n", ans);
	return 0;
}