#include <bits/stdc++.h>
using namespace std;
const int N = 5010;
double dp[N][N];
int main() {
  dp[0][0] = 1;
  int n, T;
  scanf("%d%d", &n, &T);
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    int p, t;
    scanf("%d%d", &p, &t);
    double pp = 1, tmp = (100 - p) / 100.0;
    for (int j = 1; j <= t - 1; j++) pp *= tmp;
    for (int j = t; j <= T; j++) {
      dp[i][j] = dp[i - 1][j - t] * pp;
    }
    double sum = 0;
    for (int j = 1; j <= T && t != 1; j++) {
      sum = sum + dp[i - 1][j - 1];
      dp[i][j] += sum * (1 - tmp);
      sum *= tmp;
      if (j >= t - 1) sum = sum - dp[i - 1][j - t + 1] * pp;
    }
    for (int j = 1; j <= T; j++) ans += dp[i][j];
  }
  printf("%.20lf\n", ans);
  return 0;
}
