#include <bits/stdc++.h>
const int MAXN = 5005;
const int MAX_T = 5005;
double dp[MAXN][MAX_T];
double p[MAXN];
int t[MAXN];
int main(void) {
  int n, T;
  scanf(" %d %d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf(" %lf %d", &p[i], &t[i]);
    p[i] /= 100.0;
  }
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double sum = 0;
    int left = 0;
    int right = 0;
    double prob_last_chance = pow(1 - p[i], t[i] - 1);
    for (int j = 0; j <= T; j++) {
      sum *= (1 - p[i]);
      while (right < j) {
        sum += dp[i - 1][right];
        right++;
      }
      while (right - left >= t[i]) {
        sum -= dp[i - 1][left] * prob_last_chance;
        left++;
      }
      dp[i][j] = sum * p[i];
      if (j - t[i] >= 0) {
        dp[i][j] += dp[i - 1][j - t[i]] * prob_last_chance;
      }
      ans += dp[i][j];
    }
  }
  printf("%.12f\n", ans);
  return 0;
}
