#include <bits/stdc++.h>
using namespace std;
int n, T;
double dp[5010][5010];
double p[5010];
int t[5010];
int main() {
  int i = 0, j = 0, k = 0;
  scanf("%d %d", &n, &T);
  double ans = 0.0;
  double po;
  for (i = 1; i <= n; i++) {
    scanf("%lf %d", &p[i], &t[i]);
    p[i] = p[i] / 100.0;
  }
  dp[0][0] = 1;
  for (i = 1; i <= n; i++) {
    po = pow(1 - p[i], t[i] - 1);
    for (j = i; j <= T; j++) {
      double s = dp[i][j - 1];
      if (j > t[i]) s = s - dp[i - 1][j - 1 - t[i]] * po;
      s *= (1 - p[i]);
      if (j >= t[i]) s += dp[i - 1][j - t[i]] * po * (1 - p[i]);
      s += dp[i - 1][j - 1] * p[i];
      dp[i][j] = s;
      ans += dp[i][j];
    }
  }
  printf("%.10f\n", ans);
  return 0;
}
