#include <bits/stdc++.h>
using namespace std;
int n, m, i, j, t[5555];
double dp[5555][5555], p[5555], ans;
int main() {
  cin >> n >> m;
  for (i = 1; i <= n; ++i) cin >> p[i] >> t[i], p[i] /= 100.0;
  dp[1][0] = 1;
  for (i = 1; i <= n; ++i) {
    double d = 0, pw = 1;
    for (j = 1; j < t[i]; ++j) pw *= (1 - p[i]);
    for (j = 0; j < m; ++j) {
      d = d * (1 - p[i]) + dp[i][j];
      if (j + 1 >= t[i]) d -= pw * (dp[i][j - t[i] + 1]);
      double td = d;
      td *= p[i];
      if (j + 1 >= t[i]) td += pw * (dp[i][j - t[i] + 1]);
      dp[i + 1][j + 1] = td;
      ans += td;
    }
  }
  cout << fixed << setprecision(9) << ans << endl;
  return 0;
}
