// ki bood ke goft Ghatinga?

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<pii,int> ppiii;

// vectors and Sets:
#define vc vector
#define pb push_back
#define all(c) (c).begin(), (c).end()

// pairs
#define mp make_pair
#define fr first
#define sc second

// execution time check and Debug
#define StartEX clock_t startExeTime = clock();
#define EndEX clock_t endExeTime = clock();
#define ExTime cerr << "\nTotal Execution Time is: " << double(-double(startExeTime)+double(endExeTime)) / CLOCKS_PER_SEC;
#define debug(x) cerr << #x << " : " << x << '\n'
#define endl "\n"

// time optimization
#define Heh ios::sync_with_stdio(false);cin.tie(0);
#define Bah ios::sync_with_stdio(false);
#pragma GCC optimize("Ofast")
// #pragma GCC target("avx,avx2,fma")

// useful functions
ll pw(ll a,ll b){
  ll ret = 1;
  ll mul = a;
  while(b > 0){
	if(b&1)
	  ret = (ret * mul);
	mul = (mul * mul);
	b >>= 1;
  }
  return ret;
}
ll pw(ll a,ll b,ll mod){
  ll ret = 1;
  ll mul = a;
  while(b > 0){
	if(b&1)
	  ret = (ret * mul) % mod;
	mul = (mul * mul) % mod;
	b >>= 1;
  }
  return ret;
}

ll to_int(string s){
  ll ret = 0;
  for(int i = 0 ; i < (int)s.size() ; i++) ret = 10 * ret + s[i] - '0';
  return ret;
}

bool deq(ld a , ld b){return (abs(a-b) < 0.000001);} // 10 ^ -6

const int MAXP = 1e6 + 16;

int main()
{
  int n;
  cin >> n;
  string s[n];
  for(int i = 0 ; i < n ; i++) cin >> s[i];
  for(int t = 1 ; t <= 1001 ; t++){
    int k = 0;
    int ii = -2;
    
    for(int i = 0 ; i < n ; i++){
      if(s[i].back() == '}') k--;
      
      int ci = 0;
      for(char ch : s[i]){
	if(ch == 't') ci += t;
	if(ch == 's') ci += 1;
      }
      
      if(k == 0 and ci > 0){
	ii = -1;
	break;
      }
      else if(k == 0 and ci == 0){
      }
      else if(ci == 0){
	ii = -1;
	break;
      }
      else if(ci % k > 0 or (ii != -2 and ii != ci / k)){
	ii = -1;
	break;
      }
      if(k > 0) ii = ci / k;
      
      if(s[i].back() == '{') k++;
    }
    
    if(ii != -1){
      cout << t << endl;
      break;
    }
  }

  cout << -1 << endl;
}

// ki seda kard Patinga?