#include <bits/stdc++.h>
const long long INF = 1e9;
const long long lINF = 1e18;
using namespace std;
int n, T;
double prob[5555][5555], ans;
int main() {
  cin >> n >> T;
  prob[0][0] = 1;
  int t, p2;
  double p, sum = 0, sum2 = 0;
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &p2, &t);
    p = p2 * 1.0 / 100;
    sum = 0;
    sum2 = 0;
    double pow2 = 1;
    for (int j = 0; j < t - 1; j++) pow2 *= 1 - p;
    for (int j = 1; j < t; j++) {
      sum2 *= (1 - p);
      sum2 += p * prob[i][j - 1];
      prob[i + 1][j] = sum2;
      ans += prob[i + 1][j];
    }
    for (int j = t; j <= T; j++) {
      sum2 *= (1 - p);
      sum2 += p * (prob[i][j - 1] - prob[i][j - t] * pow2);
      prob[i + 1][j] = prob[i][j - t] * pow2 + sum2;
      ans += prob[i + 1][j];
    }
  }
  printf("%.10f", ans);
  return 0;
}
