#include <bits/stdc++.h>
using namespace std;
double p[5005];
double qt[5005];
int t[5005];
double E[5005][5005];
int N, T;
double F(int i, int tym) {
  if (i >= N + 1) return 0;
  if (tym >= T) return 0;
  double& ret = E[i][tym];
  if (ret > -0.5) return ret;
  ret = 0.00;
  ret = (1 - p[i]) * F(i, tym + 1);
  ret += p[i] * (1 + F(i + 1, tym + 1));
  if (fabs(qt[i]) > 1e-15 && tym + t[i] <= T)
    ret += qt[i] * (1 + F(i + 1, tym + t[i]));
  if (fabs(qt[i]) > 1e-15 && tym + t[i] + 1 <= T)
    ret -= qt[i] * (1 + F(i + 1, tym + t[i] + 1));
  return ret;
}
int main() {
  scanf("%d%d", &N, &T);
  int i, j;
  for (i = 0; i <= N; i++) {
    for (j = 0; j <= T; j++) E[i][j] = -1.00;
  }
  for (i = 1; i <= N; i++) {
    scanf("%lf", &p[i]);
    p[i] /= 100.00;
    scanf("%d", &t[i]);
    qt[i] = pow(1.00 - p[i], t[i]);
  }
  double Ans = F(1, 0);
  printf("%.8lf\n", Ans);
  return 0;
}
