#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5010;
int N, K;
double P[MAXN];
int T[MAXN];
double dp[MAXN][MAXN];
int main() {
  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
  }
  ios_base::sync_with_stdio(false);
  cin >> N >> K;
  for (int i = 1; i <= N; i++) {
    cin >> P[i] >> T[i];
    P[i] /= 100;
  }
  double s = dp[1][1] = P[1], ans = s;
  if (T[1] == 1) {
    dp[1][1] = ans = 1;
  } else {
    for (int i = 2; i <= T[1]; i++) {
      if (i == T[1]) {
        dp[1][i] = 1 - s;
      } else {
        dp[1][i] = dp[1][i - 1] * (1 - P[1]);
        s += dp[1][i];
      }
      ans += dp[1][i];
    }
  }
  for (int i = 2; i <= N; i++) {
    double p = P[i], q = 1 - p;
    int t = T[i];
    double pwr = pow(q, t - 1);
    for (int j = 1; j <= K; j++) {
      double &ref = dp[i][j];
      ref = dp[i][j - 1] * q + dp[i - 1][j - 1] * p;
      if (j > t) {
        ref += pwr * q * (dp[i - 1][j - t] - dp[i - 1][j - t - 1]);
      }
      if (ref < 1e-15) {
        ref = 0;
      } else {
        ans += ref;
      }
    }
  }
  cout << setprecision(9) << ans << endl;
}
