#include <bits/stdc++.h>
using namespace std;
int n;
int in[4];
string s[10001];
int temp;
int chengF(int x, int y) {
  int i;
  for (i = 1; i <= y; i++) {
    x *= 10;
  }
  return x;
}
int main() {
  in[0] = -2000000000;
  in[1] = in[0];
  in[2] = 2000000000;
  in[3] = in[2];
  int i, j, k;
  cin >> n;
  for (i = 0; i < n; i++) {
    temp = 0;
    if (i == 0) cin.ignore(1024, '\n');
    getline(cin, s[i]);
    if (s[i][s[i].length() - 1] == 'N') {
      if (s[i][0] == '>' && s[i][1] != '=') {
        s[i][0] = '<';
        s[i][1] = '=';
      } else if (s[i][0] == '>' && s[i][1] == '=') {
        s[i][0] = '<';
        s[i][1] = ' ';
      } else if (s[i][0] == '<' && s[i][1] != '=') {
        s[i][0] = '>';
        s[i][1] = '=';
      } else if (s[i][0] == '<' && s[i][1] == '=') {
        s[i][0] = '>';
        s[i][1] = ' ';
      }
    }
    if (s[i][0] == '>' && s[i][1] != '=') {
      for (j = s[i].length() - 3, k = 0;
           ('0' <= (int)s[i][j] && (int)s[i][j] <= '9') || s[i][j] == '-';
           j--, k++) {
        if (s[i][j] == '-')
          temp = -temp;
        else
          temp += chengF((int)s[i][j] - '0', k);
      }
      if (temp > in[0]) {
        in[0] = temp;
      }
    } else if (s[i][0] == '>' && s[i][1] == '=') {
      for (j = s[i].length() - 3, k = 0;
           ('0' <= (int)s[i][j] && (int)s[i][j] <= '9') || s[i][j] == '-';
           j--, k++) {
        if (s[i][j] == '-')
          temp = -temp;
        else
          temp += chengF((int)s[i][j] - '0', k);
      }
      if (temp > in[1]) {
        in[1] = temp;
      }
    } else if (s[i][0] == '<' && s[i][1] != '=') {
      for (j = s[i].length() - 3, k = 0;
           ('0' <= (int)s[i][j] && (int)s[i][j] <= '9') || s[i][j] == '-';
           j--, k++) {
        if (s[i][j] == '-')
          temp = -temp;
        else
          temp += chengF((int)s[i][j] - '0', k);
      }
      if (temp < in[2]) {
        in[2] = temp;
      }
    } else if (s[i][0] == '<' && s[i][1] == '=') {
      for (j = s[i].length() - 3, k = 0;
           ('0' <= (int)s[i][j] && (int)s[i][j] <= '9') || s[i][j] == '-';
           j--, k++) {
        if (s[i][j] == '-')
          temp = -temp;
        else
          temp += chengF((int)s[i][j] - '0', k);
      }
      if (temp < in[3]) {
        in[3] = temp;
      }
    }
  }
  if (in[0] >= in[2] - 1 || in[0] >= in[3] || in[1] >= in[2] || in[1] > in[3]) {
    cout << "Impossible" << endl;
  } else {
    if (in[0] < in[1]) {
      if (in[2] > in[3]) {
        cout << in[1] << endl;
      } else {
        cout << in[1] << endl;
      }
    } else {
      if (in[2] > in[3]) {
        cout << in[3] << endl;
      } else {
        cout << in[2] - 1 << endl;
      }
    }
  }
  return 0;
}
