#include <bits/stdc++.h>
using namespace std;
double dp[2][5005];
double p[5005];
int d[5005];
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 0; i < n; i++) cin >> p[i] >> d[i];
  int cur = 0, pre = 1;
  for (int i = n - 1; i >= 0; i--) {
    p[i] /= 100;
    double tot = 0;
    double tmp[5005] = {};
    for (int t = 1; t <= T; t++) {
      tot = (1 - p[i]) * tot + p[i] * (1 + dp[pre][t - 1]);
      tmp[t] = dp[cur][t] = tot;
      if (t >= d[i])
        dp[cur][t] +=
            pow(1.0 - p[i], d[i]) * (1 + dp[pre][t - d[i]] - tmp[t - d[i]]);
    }
    cur ^= 1, pre ^= 1;
  }
  printf("%.8lf\n", dp[pre][T]);
  return 0;
}
