#include <bits/stdc++.h>
using namespace std;
int n, T, t[5005];
double dp[5005][5005], ans, p[5005];
double poww(double x, int num) {
  double res = 1.0;
  while (num) {
    if (num & 1) res *= x;
    x *= x;
    num >>= 1;
  }
  return res;
}
int main() {
  scanf("%d %d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf %d", &p[i], &t[i]);
    p[i] /= 100;
  }
  dp[0][0] = 1.0;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double sum = poww(1 - p[i], t[i] - 1), psum = 0;
    for (int j = 1; j <= T; j++) {
      psum *= 1 - p[i];
      psum += dp[i - 1][j - 1] * p[i];
      if (j >= t[i]) {
        psum -= dp[i - 1][j - t[i]] * sum * p[i];
        dp[i][j] += dp[i - 1][j - t[i]] * sum;
      }
      dp[i][j] += psum;
      ans += dp[i][j];
    }
  }
  printf("%.7lf\n", ans);
  return 0;
}
