#include <bits/stdc++.h>
using namespace std;
int n, t, i, j;
pair<int, int> a[5005];
double dp[5005][5005];
int main() {
  scanf("%d%d", &n, &t);
  for (i = 1; i <= n; i++) scanf("%d%d", &a[i].first, &a[i].second);
  dp[0][0] = 1.0;
  double ans = 0.0;
  for (i = 1; i <= n; i++) {
    double ok = a[i].first * 1.0 / 100;
    double nok = 1.0 - ok;
    double now = dp[i - 1][0];
    double p = pow(nok, a[i].second - 1);
    for (j = 1; j <= t; j++) {
      if (j >= a[i].second) {
        now -= dp[i - 1][j - a[i].second] * p;
        dp[i][j] += dp[i - 1][j - a[i].second] * p;
      }
      dp[i][j] += now * ok;
      ans += dp[i][j];
      now = now * nok + dp[i - 1][j];
    }
  }
  printf("%.12lf\n", ans);
}
