#include <bits/stdc++.h>
using namespace std;
const int maxn = (int)5e5 + 10;
const int mod = (int)1e9 + 7;
const int inf = (1 << 30) - 1;
double dp[5050];
double d[5050];
int n, T;
double pref[5050];
void solve() {
  dp[0] = 1;
  cin >> n >> T;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    int P, t;
    cin >> P >> t;
    double p = P / 100.0;
    double q = 1 - p;
    double x = 1;
    for (int j = 1; j < t; j++) x *= q;
    for (int j = 0; j <= T; j++) {
      d[j] = dp[j];
      dp[j] = 0;
    }
    double s = 0;
    for (int j = 1; j <= T; j++) {
      s = s * q + d[j - 1] * p;
      if (j >= t) {
        s -= x * d[j - t] * p;
        dp[j] = d[j - t] * x + s;
      } else {
        dp[j] = s;
      }
      ans += dp[j];
    }
  }
  printf("%.12lf\n", ans);
}
int main() {
  int t = 1;
  for (int i = 1; i <= t; i++) {
    solve();
  }
  return 0;
}
