#include <bits/stdc++.h>
using namespace std;
int n, m;
double tbl[5001][5001];
int p[5001];
int t[5001];
inline double pow(double x, int y) {
  double r = 1.0;
  while (y) {
    if (y % 2) r *= x;
    x *= x;
    y /= 2;
  }
  return r;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> m;
  for (int i = 0; i < n; ++i) cin >> p[i] >> t[i];
  tbl[0][0] = 1.0;
  double acc = 0.0;
  for (int i = 0; i < n; ++i) {
    double win = p[i] / 100.0;
    double lose = 1.0 - win;
    double lose_t = pow(lose, t[i] - 1);
    double win_t = lose_t * win;
    double prob = 0.0;
    for (int j = 0; j < m; ++j) {
      prob = prob * lose + tbl[i][j] * win;
      if (j + 1 >= t[i]) {
        prob -= tbl[i][j + 1 - t[i]] * win_t;
        tbl[i + 1][j + 1] = prob + tbl[i][j + 1 - t[i]] * lose_t;
      } else {
        tbl[i + 1][j + 1] = prob;
      }
    }
    for (int j = 0; j <= m; ++j) acc += tbl[i + 1][j];
  }
  cout << fixed << setprecision(8) << acc << endl;
  return 0;
}
