#include <bits/stdc++.h>
using namespace std;
double dp[2][5005];
int n, T;
double p[5005];
int t[5005];
int main() {
  scanf("%d%d", &n, &T);
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) scanf("%lf%d", p + i, t + i), p[i] /= 100;
  int s = 1;
  for (int i = 1; i <= n; i++) {
    double e = pow(1 - p[i], t[i]);
    double tmp = 0;
    for (int j = 0; j <= T; j++) {
      if (j - 1 >= 0) tmp += dp[s ^ 1][j - 1];
      if (j - t[i] - 1 >= 0) tmp -= dp[s ^ 1][j - t[i] - 1] * e;
      dp[s][j] = tmp * p[i];
      if (j - t[i] >= 0) dp[s][j] += dp[s ^ 1][j - t[i]] * e;
      tmp *= (1 - p[i]);
      ans += dp[s][j];
    }
    s ^= 1;
  }
  printf("%.11lf\n", ans);
  return 0;
}
