#include <bits/stdc++.h>
using namespace std;
double p[5006], dp[5006][5006], ans = 0;
int t[5006], n, T;
int main() {
  memset(dp, 0, sizeof(dp));
  memset(p, 0, sizeof(p));
  ios_base::sync_with_stdio(false);
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100;
  }
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double res = 0, q = pow(1 - p[i], t[i] - 1);
    for (int j = 0; j <= T; j++) {
      if (j >= t[i]) {
        dp[i][j] += dp[i - 1][j - t[i]] * q;
        res -= dp[i - 1][j - t[i]] * q;
      }
      dp[i][j] += res * p[i];
      res *= (1 - p[i]);
      if (j < T) res += dp[i - 1][j];
    }
    dp[i - 1][T] += res;
  }
  for (int i = 1; i <= n; i++) ans += dp[i][T] * i;
  for (int i = 1; i < T; i++) ans += dp[n][i] * n;
  cout << fixed << setprecision(10) << ans;
}
