#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define int ll
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
using pii = pair<int, int>;
using vi = vector<int>;
#define fi first
#define se second
#define pb push_back

struct Line {int S,T,I;};

vector<Line> lines;

bool check(int t)
{
    int i=-1;
    for(auto[S,T,I]:lines)
    {
        int num=S+T*t,den=I;
        if(den==0)
        {
            if(num!=0)
                return false;
        }
        else
        {
            if(num%den!=0)
                return false;
            if(i==-1)
                i=num/den;
            else if(i!=num/den)
                return false;
        }
    }
    return true;
}

signed main() {
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(cin.failbit);

    int n;
    cin>>n;
    int depth=0;
    while(n--)
    {
        string line;
        cin>>line;
        int S=0,T=0;
        for(char c:line)
            if(c=='s')
                S++;
            else if(c=='t')
                T++;
        int I;
        if(line.back()=='{')
        {
            I=depth;
            depth++;
        }
        else
        {
            depth--;
            I=depth;
        }
        lines.pb({S,T,I});
    }
    for(int t=1;clock()*1.0/CLOCKS_PER_SEC<0.9;t++)
        if(check(t))
            cout<<t,exit(0);
    cout<<-1;
}