#include <bits/stdc++.h>
using namespace std;
double dp[5][5005];
double p[5005], subp[5005];
int t[5005];
double qpow(double a, int k) {
  double res = 1;
  while (k) {
    if (k & 1) res *= a;
    a *= a;
    k >>= 1;
  }
  return res;
}
int main(int argc, const char* argv[]) {
  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;
    subp[i] = 1 - p[i];
  }
  int cur = 1;
  dp[cur ^ 1][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; ++i, cur ^= 1) {
    double pp = pow(subp[i], t[i] - 1);
    dp[cur][0] = 0;
    for (int j = 1; j <= T; ++j) {
      double tmp = dp[cur][j - 1];
      if (j - 1 >= t[i]) tmp -= dp[cur ^ 1][j - 1 - t[i]] * pp;
      tmp *= subp[i];
      if (j >= t[i]) tmp += dp[cur ^ 1][j - t[i]] * subp[i] * pp;
      tmp += dp[cur ^ 1][j - 1] * p[i];
      dp[cur][j] = tmp;
      ans += tmp;
    }
  }
  printf("%.10f\n", ans);
  return 0;
}
