#include <bits/stdc++.h>
using namespace std;
double dp[5100];
int p[5100], t[5100];
double temp[5100][2];
int main() {
  int n, T;
  scanf("%d%d", &n, &T);
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &p[i], &t[i]);
  }
  for (int i = 0; i <= T; i++) {
    dp[i] = 1.0;
  }
  double ans = 0, anstemp = 0;
  for (int i = 0; i < n; i++) {
    temp[0][0] = temp[0][1] = 0;
    double x = pow((100 - p[i]) * 0.01, t[i] - 1);
    for (int j = 1; j <= T; j++) {
      temp[j][0] =
          temp[j - 1][0] * (100 - p[i]) * 0.01 + dp[j - 1] * p[i] * 0.01;
      if (j >= t[i]) {
        temp[j][0] -= dp[j - t[i]] * x * p[i] * 0.01;
        temp[j][1] = dp[j - t[i]] * x;
      }
    }
    for (int j = T; j >= 0; j--) {
      dp[j] = temp[j][0];
      if (j >= t[i]) dp[j] += temp[j][1];
    }
    ans += dp[T];
  }
  printf("%.6lf\n", ans);
}
