#include <bits/stdc++.h>
using namespace std;
int t, n;
int tt[5005];
double p[5005];
double dp[5050][5050];
double fpow(double x, int a) {
  double ans = 1;
  while (a) {
    if (a & 1) ans *= x;
    x *= x;
    a >>= 1;
  }
  return ans;
}
int main() {
  scanf("%d%d", &n, &t);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &tt[i]);
    p[i] /= 100;
  }
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double sum = 0;
    double kth = fpow(1 - p[i], tt[i] - 1);
    for (int j = 1; j <= t; j++) {
      sum *= 1 - p[i];
      sum += dp[i - 1][j - 1] * p[i];
      if (j >= tt[i]) {
        sum -= dp[i - 1][j - tt[i]] * kth * p[i];
        dp[i][j] += dp[i - 1][j - tt[i]] * kth;
      }
      dp[i][j] += sum;
      ans += dp[i][j];
    }
  }
  printf("%.7f\n", ans);
  return 0;
}
