#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
double p[5005];
int t[5005];
int n, T;
double dp[5005][5005];
double pow(double x, int y) {
  double res = 1;
  for (int j = 0; j < y; j++) res = res * x;
  return res;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100;
  }
  cout << fixed << setprecision(8);
  for (int i = n; i >= 1; i--) {
    double cal = 0;
    double f = pow(1 - p[i], t[i]);
    for (int x = 1; x <= T; x++) {
      cal *= (1 - p[i]);
      if (x > t[i]) cal -= f * p[i] * (1 + dp[i + 1][x - t[i] - 1]);
      cal += p[i] * (1 + dp[i + 1][x - 1]);
      dp[i][x] = cal;
      if (x >= t[i]) dp[i][x] += f * (1 + dp[i + 1][x - t[i]]);
    }
  }
  cout << dp[1][T] << "\n";
}
