#include <bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define pl pair<ll, ll>
#define pi pair<int, int>
#define minpq priority_queue<ll, vector<ll>, greater<ll>>
using namespace std;

#if 1
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '['; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "]";}
void _print() {cerr << endl << flush;}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#define debug(x...) cerr << "*["<<__LINE__<<"]\t"<< #x << " = "; _print(x)
#endif

const ll mod = 1e9 + 7;

template<typename T> bool chkmin(T &a, T b){return (b < a) ? a = b, 1 : 0;}
template<typename T> bool chkmax(T &a, T b){return (b > a) ? a = b, 1 : 0;}
ll gcd(ll a, ll b) {if(b == 0){return a;} return gcd(b, a % b);}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n; cin >> n;
	vector<string> a(n); for (int i = 0; i < n; i ++) cin >> a[i];
	vector<bool> open(n); for (int i = 0; i < n; i ++) open[i] = a[i][a[i].size() - 1] == '{';
	vector<int> dep(n);
	for (int i = 1; i < n; i ++){
		if (open[i] && open[i - 1]){
			dep[i] = dep[i - 1] + 1;
		} else if (open[i] && !open[i - 1] || !open[i] && open[i - 1]){
			dep[i] = dep[i - 1];
		} else{
			dep[i] = dep[i - 1] - 1;
		}
	}
	int maxtry = 100000;
	vector<int> cnts(n), cntt(n);
	for (int i = 0; i < n; i ++){
		for (int j = 0; j < a[i].size(); j ++){
			if (a[i][j] == 's') cnts[i] ++;
			if (a[i][j] == 't') cntt[i] ++;
		}
	}
	for (int i = 1; i <= maxtry; i ++){
		int cur = -1;
		bool good = true;
		for (int j = 0; j < n; j ++){
			if (cntt[j] == 0){
				if (i * dep[j] != cnts[j]){
					good = false; break;
				} else continue;
			}
			if (i * dep[j] <= cnts[j] || (i * dep[j] - cnts[j]) % cntt[j] != 0){
				good = false;
				break;
			}
			if (cur == -1) cur = (i * dep[j] - cnts[j]) / cntt[j];
			else{
				if (cur != (i * dep[j] - cnts[j]) / cntt[j]){
					good = false;
					break;
				}
			}
		}
		if (good){
			cout << cur << '\n';
			return 0;
		}
	}
	cout << -1 << '\n';
}

/*
Do something instead of nothing!
Print out stuffs / study samples when you cannot find the bug!
*/