#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
int n, T, t[N];
double dp[N][N], p[N];
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> T;
  int tmp;
  for (int i = 1; i <= n; i++) cin >> tmp >> t[i], p[i] = tmp / 100.0;
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double sum = p[i] * dp[i - 1][0], pre = 0;
    double pw = pow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      if (j >= t[i]) {
        pre = pre * (1 - p[i]) + dp[i - 1][j - t[i]] * p[i] * pw;
        dp[i][j] = dp[i - 1][j - t[i]] * pw;
      }
      dp[i][j] += sum - pre;
      sum = sum * (1 - p[i]) + dp[i - 1][j] * p[i];
      ans += dp[i][j];
    }
  }
  printf("%.10lf", ans);
  return 0;
}
