#include <bits/stdc++.h>
using namespace std;
int prob[5000], times[5000];
double dp[5005][5005];
double fastpow(double x, int n) {
  double y = 1;
  while (n) {
    if (n & 1) y *= x;
    x *= x;
    n >>= 1;
  }
  return y;
}
int main() {
  ios_base::sync_with_stdio(false);
  int n, T;
  scanf("%d %d", &n, &T);
  for (int i = 0; i < n; ++i) {
    scanf("%d %d", &prob[i], &times[i]);
  }
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; ++i) {
    double p = prob[i - 1] * .01;
    int ti = times[i - 1];
    double pexp = fastpow(1 - p, ti);
    double now = 0;
    for (int j = 1; j <= T; ++j) {
      now = now * (1 - p) + dp[i - 1][j - 1] * p;
      if (j >= ti) {
        now -= dp[i - 1][j - ti - 1] * pexp;
        now += dp[i - 1][j - ti] * pexp;
      }
      ans += now;
      dp[i][j] = now;
    }
  }
  printf("%.12f\n", ans);
}
