#include <bits/stdc++.h>
using namespace std;
double d[5001][5001] = {};
int pp[5001], t[5001];
int n, T;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> T;
  for (int i = 0; i < (int)(n); ++i) cin >> pp[i] >> t[i];
  d[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    double p = 0.01 * pp[i - 1];
    double q = 1 - p;
    int cnt = t[i - 1];
    double mul2 = 1;
    for (int j = 0; j < (int)(cnt - 1); ++j) mul2 *= q;
    double mul = mul2 * p;
    double cur = 0;
    for (int j = 1; j <= T; ++j) {
      cur = q * cur + p * d[i - 1][j - 1];
      if (cur < 1e-30) cur = 0;
      if (j >= cnt) {
        cur -= mul * d[i - 1][j - cnt];
        d[i][j] = d[i - 1][j - cnt] * mul2;
      }
      d[i][j] += cur;
      if (d[i][j] < 1e-30) d[i][j] = 0;
    }
  }
  double ans = 0;
  for (int i = 1; i <= n; ++i) {
    double mul = i;
    double q = (i == n) ? 1.0 : (1.0 - 0.01 * pp[i]);
    int cnt = (i == n) ? 100000 : t[i];
    for (int j = T; j > max(-1, T - cnt); --j) {
      ans += mul * d[i][j];
      mul *= q;
      if (mul < 1e-30) break;
    }
  }
  cout << setprecision(12) << fixed << ans << endl;
  return 0;
}
