#include <bits/stdc++.h>
using namespace std;
const int maxn = 5000 + 100;
long double dp[2][maxn];
long double p[maxn];
int t[maxn];
long double mypow(long double a, int b) {
  if (b == 0) return 1;
  long double mid = mypow(a, b / 2);
  mid *= mid;
  return b % 2 ? a * mid : mid;
}
int main() {
  ios_base::sync_with_stdio(false);
  int n, T;
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100;
  }
  for (int i = n; i > 0; i--) {
    long double sum = 0;
    long double pt1 = mypow(1 - p[i], t[i] - 1);
    long double pt2 = mypow(1 - p[i], t[i] - 2);
    for (int j = 1; j <= T; j++) {
      if (t[i] == 1) {
        dp[i % 2][j] = dp[(i + 1) % 2][j - 1] + 1;
        continue;
      }
      if (j >= t[i]) sum -= (1 + dp[(i + 1) % 2][j - t[i]]) * pt2 * p[i];
      sum *= (1 - p[i]);
      sum += (1 + dp[(i + 1) % 2][j - 1]) * p[i];
      dp[i % 2][j] = sum;
      if (j >= t[i]) dp[i % 2][j] += pt1 * (1 + dp[(i + 1) % 2][j - t[i]]);
    }
  }
  cout << fixed << setprecision(7) << dp[1][T] << endl;
  return 0;
}
