#include <bits/stdc++.h>
using namespace std;
int n, T;
double dp[5555][5555];
double p[5555], pp[5555];
int t[5555];
int main() {
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100.0;
  }
  for (int i = 1; i <= n; i++) {
    pp[i] = pow(1 - p[i], t[i] - 1.0);
  }
  for (int i = 1; i <= T; i++) {
    for (int j = 1; j <= n; j++) {
      if (i < t[j])
        dp[i][j] = (dp[i - 1][j + 1] + 1) * p[j] + dp[i - 1][j] * (1 - p[j]);
      else {
        double tt = dp[i - 1][j];
        if (i - 1 - t[j] >= 0) tt -= (dp[i - 1 - t[j]][j + 1] + 1) * pp[j];
        tt *= (1.0 - p[j]);
        tt += (dp[i - t[j]][j + 1] + 1) * pp[j] * (1 - p[j]);
        tt += (dp[i - 1][j + 1] + 1) * p[j];
        dp[i][j] = tt;
      }
    }
  }
  printf("%.9f\n", dp[T][1]);
  return 0;
}
