#include<bits/stdc++.h>
#define pb push_back
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
#define endl '\n'
#define fir first
#define sec second
#define file(__a) freopen(__a".in","r",stdin),freopen(__a".out","w",stdout);
#define look_time cerr<<(clock()-Time)/1000.0<<"s"<<endl
#define look_memory cerr<<(&b2-&b1)/1024.0/1024.0<<"MB"<<endl
using namespace std;
bool b1;
time_t Time = clock();
int T = 1;
template<typename T>
inline void read(T &s) {
	T f = 1, c = 0;
	char ch = getchar();
	while (!isdigit(ch)) {
		if (ch == '-') {
			f = -1;
		}
		ch = getchar();
	}
	while (isdigit(ch)) {
		c = (c << 1) + (c << 3) + (ch ^ 48);
		ch = getchar();
	}
	s = f * c;
}
template<typename T, typename ...Args>
inline void read(T &s, Args &...args) {
	read(s), read(args...);
}
namespace white_carton {
int n, x, y;
struct node {
	int x, y;
	char ch;
	int id;
} a[1001000];
bool cmp(node a, node b) {
	return a.x < b.x;
}
void Solve() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> x >> y;
		cin >> a[i].ch;
		x = x * 2;
		a[i].x = x + y + 3e8 + 1;
		a[i].y = y - x + 3e8 + 1;
		a[i].id = i;
	}
	sort(a + 1, a + 1 + n, cmp);
	int minn = INF;
	for (int i = 1; i <= n; i++) {
		int l = i, r = i;
		while (a[r].x == a[r + 1].x) {
			r++;
		}
		for (int j = l; j <= r; j++) {
			if (a[j].ch == 'N') {
				minn = min(minn, a[j].y);
			}
		}
		for (int j = l; j <= r; j++) {
			if (a[j].ch == 'P' && a[j].y >= minn) {
				cout << "impossible" << endl;
				return;
			}
			if (a[j].ch == '-' && a[j].y >= minn) {
				a[j].ch = 'N';
			}
		}
		i = r;
	}
	int MAXN = -INF, MAXN_ = -INF;
	int ans = 0;
	for (int i = n; i >= 1; i--) {
		int l = i, r = i;
		while (l > 1 && a[l].x == a[l - 1].x) {
			l--;
		}
		for (int i = l; i <= r; i++) {
			if (a[i].ch == 'N') {
				continue;
			}
			MAXN_ = max(MAXN_, a[i].y);
		}
		// cout << MAXN_ << endl;
		for (int i = l; i <= r; i++) {
			if (a[i].ch == 'N') {
				continue;
			}
			if (a[i].y > MAXN && a[i].ch == 'P') {
				ans++;
				MAXN = MAXN_;
			}
		}
		i = l;
	}
	cout << ans << endl;
}
}

bool b2;
signed main() {
	// file("dis");
	// cin>>T;
	while (T--)white_carton::Solve();
	look_time;
	look_memory;
}
//日拱一卒，功不唐捐