#include <bits/stdc++.h>
using namespace std;
long long int power(long long int x, long long int y) {
  long long int temp;
  if (y == 0) return 1;
  temp = power(x, y / 2);
  if (y % 2 == 0)
    return (temp * temp);
  else {
    if (y > 0)
      return (((x * temp) % 1000000007) * temp);
    else
      return (temp * temp) / x;
  }
}
long long int mul_inv(long long int n, long long int p, long long int m) {
  if (p == 1) {
    return n % m;
  } else if (p % 2 == 0) {
    long long int t = mul_inv(n, p / 2, m);
    return ((t) * (t)) % m;
  } else {
    long long int t = mul_inv(n, p / 2, m);
    return ((((n % m) * t) % m) * t) % m;
  }
}
bool isprime(long long int n) {
  if (n == 2) {
    return true;
  }
  if (n % 2 == 0) {
    return false;
  }
  for (long long int i = 3; i <= sqrt(n); i += 2) {
    if (n % i == 0) {
      return false;
    }
  }
  return true;
}
double P[5005][5005];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  P[0][0] = 1;
  int n, T;
  cin >> n >> T;
  double ans = 0;
  for (int i = 0; i < n; i++) {
    int t;
    double p;
    cin >> p >> t;
    p /= 100;
    double q = pow(1 - p, t - 1);
    double temp = 0;
    for (int j = 1; j <= T; ++j) {
      if (j < t) {
        temp *= (1 - p);
        temp += P[i][j - 1] * p;
        P[i + 1][j] = temp;
      } else {
        temp *= (1 - p);
        temp += P[i][j - 1] * p;
        temp -= P[i][j - t] * p * q;
        P[i + 1][j] = temp;
        P[i + 1][j] += P[i][j - t] * q;
      }
      ans += P[i + 1][j];
    }
  }
  cout << std::fixed;
  cout << std::setprecision(9);
  cout << ans;
  return 0;
}
