#include <bits/stdc++.h>
using namespace std;
double p[5005], dp[2][5005];
int t[5005];
int main() {
  int n, T;
  scanf("%d%d", &n, &T);
  for (int i = 1, tp; i <= n; i++) {
    scanf("%d%d", &tp, &t[i]);
    p[i] = tp / 100.0;
  }
  double res = 0;
  int now = 0, la = 1;
  dp[now][0] = 1;
  for (int i = 1; i <= n; i++) {
    swap(now, la);
    memset(dp[now], 0, sizeof(dp[now]));
    double cof = pow(1 - p[i], t[i] - 1), tmp = 0;
    for (int j = t[i]; j <= T; j++) dp[now][j] += dp[la][j - t[i]] * cof;
    cof = pow(1 - p[i], t[i] - 2) * p[i];
    if (t[i] > 1)
      for (int j = 0; j <= T; j++) {
        dp[now][j] += tmp;
        if (j >= t[i] - 1) tmp -= dp[la][j - t[i] + 1] * cof;
        tmp = tmp * (1 - p[i]) + dp[la][j] * p[i];
      }
    for (int j = 0; j <= T; j++) res += dp[now][j];
  }
  return 0 * printf("%.9f", res);
}
