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

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define rep(i,a,b) for(auto i=(a); i<(b); ++i)
#define REP(i,n) rep(i,0,n)
#define all(v) begin(v), end(v)
#define sz(v) ((int) (v).size())
#define rs resize
#define DBG(x) cerr << __LINE__ << ": " \
		<< #x<< " = " << (x) << endl

template<class T> ostream& operator<<(ostream &os,
		const vector<T> &v) {
	os << "\n[";
	for(const T &x : v) os << x << ',';
	return os << "]\n";
}

namespace std { template<class T1, class T2>
struct hash<pair<T1,T2>> { public:
	size_t operator()(const pair<T1,T2> &p) const {
		size_t x = hash<T1>()(p.x), y = hash<T2>()(p.y);
		return x ^ (y + 0x9e3779b9 + (x<<6) + (x>>2));
	}
}; }

void run() {
	ll n;
	cin >> n;
	unordered_map<string, ll> A;
	ll res = 0;
	bool rb = false;
	for (ll i = 0; i < n; i++) {
		string t, f;
		ll k;
		cin >> t >> f >> k;
		if (A[t] > 0 || (f == "any" && k > 1)) {
			rb = true;
		}
		if (f == "any") {
			k = 1;
		}
		res += max(k, A[t]) - A[t];
		A[t] = max(k, A[t]);
	}
	if (rb) {
		cout << res+1 << endl;
	} else {
		cout << "impossible" << endl;
	}
}

signed main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout << fixed << setprecision(20);
	run();
	return 0;
}