#include <bits/stdc++.h>
using namespace std;
double p[5005], dp[5005][5005];
int t[5005];
double Pow(double x, int k) {
  double ans = 1;
  while (k) {
    if (k % 2) ans = ans * x;
    x = x * x;
    k /= 2;
  }
  return ans;
}
int main(void) {
  double now, ans, temp;
  int n, T, i, j, k;
  scanf("%d%d", &n, &T);
  for (i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  dp[0][0] = 1, ans = 0;
  for (i = 1; i <= n; i++) {
    now = 0;
    temp = Pow(1 - p[i], t[i] - 1);
    for (j = 1; j <= T; j++) {
      now *= 1 - p[i];
      now += dp[i - 1][j - 1] * p[i];
      if (j >= t[i]) now -= dp[i - 1][j - t[i]] * temp * p[i];
      dp[i][j] = now;
      if (j >= t[i]) dp[i][j] += dp[i - 1][j - t[i]] * temp;
      ans += dp[i][j];
    }
  }
  printf("%.10f\n", ans);
  return 0;
}
