#include <bits/stdc++.h>

#define f first
#define s second
#define sz(s) (int)s.size()
#define int long long

using namespace std;

const int N = (int)5e5 + 100;
const int M = N + 7;
const int MOD = 998244353;
const int INF = (int)1e18 + 100;


int n, cnt[N][2];

main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
    cin >> n;
    int bal = 0;
    set<int> u;
    for(int i = 1; i <= n; i++){
    	string s;
        cin >> s;
        int d = 1;
        for(auto x : s){
            if(x == 's')
                cnt[i][0]++;
            if(x == 't')
                cnt[i][1]++;
            if(x == '{')
                d = 1;
            else
                d = -1;
        }
        if(d == -1) bal += d;
        
        if(cnt[i][0] || cnt[i][1]){
        	int delta = bal - cnt[i][1];
        	if(delta){
        		int c = cnt[i][0] / (bal - cnt[i][1]);
        		if(cnt[i][0] % c || cnt[i][0] < c){
        			cout << "-1\n";
        			return 0;
        		}
        		u.insert(c);
        	}
        }

        if(d == 1) bal += d;
    }
    if(u.size() != 1) cout << "-1\n";
	else{
		cout << *u.begin() << "\n";
	}
}