#include <bits/stdc++.h>
using namespace std;
double dp[5005][5005], p[5005];
int t[5005];
double quickPow(double a, int b) {
  double ans = 1.0;
  while (b) {
    if (b & 1) {
      ans = ans * a;
    }
    a = a * a;
    b >>= 1;
  }
  return ans;
}
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100.0;
  }
  dp[0][0] = 1;
  double ans = 0;
  double sum;
  double index;
  for (int i = 1; i <= n; i++) {
    sum = 0;
    index = quickPow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      sum *= 1 - p[i];
      sum += dp[i - 1][j - 1] * p[i];
      if (j >= t[i]) {
        sum -= dp[i - 1][j - t[i]] * index * p[i];
        dp[i][j] += dp[i - 1][j - t[i]] * index;
      }
      dp[i][j] += sum;
      ans += dp[i][j];
    }
  }
  printf("%.10lf", ans);
  return 0;
}
