#include <bits/stdc++.h>
using namespace std;
double dp[5002][5002], P[5002];
int t[5002];
int main() {
  int n, T;
  scanf("%d %d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf %d", &P[i], &t[i]);
    P[i] /= 100.0;
  }
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double np = 1 - P[i], temp = 0, p = P[i], mnp = pow(np, t[i] - 1);
    for (int j = 1; j <= T; j++) {
      temp *= np;
      if (j - t[i] + 1 >= 0) temp -= (dp[i - 1][j - t[i]] * mnp * p);
      temp += dp[i - 1][j - 1] * p;
      dp[i][j] = temp;
      if (j - t[i] >= 0) dp[i][j] += dp[i - 1][j - t[i]] * mnp;
      ans += dp[i][j];
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
