#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 5;
const long long linf = 1e18 + 5;
const int N = 5000 + 5;
int n, t, a[N];
double p[N], dp[2][N];
int main() {
  ios ::sync_with_stdio(0);
  cin >> n >> t;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> a[i];
    p[i] /= 100;
  }
  dp[0][0] = 1;
  double ans = 0;
  bool k = 1;
  for (int i = 1; i <= n; i++) {
    double prod = 1, last = 0, q = 1 - p[i];
    for (int j = 1; j <= a[i] - 1; j++) prod *= q;
    dp[k][0] = 0;
    for (int j = 1; j <= a[i] - 1; j++) {
      dp[k][j] = last * q + dp[!k][j - 1] * p[i];
      last = dp[k][j];
      ans += dp[k][j];
    }
    for (int j = a[i]; j <= t; j++) {
      dp[k][j] = last * q + dp[!k][j - 1] * p[i] -
                 dp[!k][j - a[i] - 1] * prod * q * p[i];
      last = dp[k][j];
      dp[k][j] += dp[!k][j - a[i]] * prod - dp[!k][j - a[i]] * prod * p[i];
      ans += dp[k][j];
    }
    k = !k;
  }
  cout << fixed << setprecision(9) << ans << '\n';
  return 0;
}
