#include <bits/stdc++.h>
using namespace std;
int n, T;
int ti[5010];
double prob[5010];
double dp[5010][5010];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &prob[i], &ti[i]);
    prob[i] /= 100;
  }
  double res = 0;
  dp[0][0] = 1;
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    sum += ti[i];
    double tmp = 0;
    double p = prob[i];
    if (p == 1) {
      ti[i] = 1;
      p = 0;
    }
    double pwer = pow(1 - p, ti[i] - 2);
    for (int j = i; j <= min(T, sum); j++) {
      if (j >= ti[i] && ti[i] != 1) tmp -= dp[i - 1][j - ti[i]] * p * pwer;
      tmp *= 1 - p;
      if (ti[i] >= 2) tmp += dp[i - 1][j - 1] * p;
      dp[i][j] = tmp;
      if (j >= ti[i]) {
        dp[i][j] += dp[i - 1][j - ti[i]] * pwer * (1 - p);
      }
      res += dp[i][j];
    }
  }
  cout << fixed << setprecision(10) << res;
  return 0;
}
