#include <bits/stdc++.h>
using namespace std;
int n, T, t[5010];
double p[5010], f[5010][5010], tmp[5010];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) scanf("%lf%d", &p[i], &t[i]), p[i] /= 100.0;
  f[1][1] = 1.0;
  T++;
  p[n + 1] = 0;
  t[n + 1] = 5010;
  for (int i = 1; i <= n + 1; i++) {
    double fac = 1;
    for (int j = 1; j <= t[i]; j++) fac *= (1.0 - p[i]);
    for (int j = 1; j <= T; j++) tmp[j] = f[i][j];
    for (int j = 1; j <= T; j++) {
      f[i][j + 1] += f[i][j] * (1.0 - p[i]);
      f[i + 1][j + 1] += f[i][j] * p[i];
      if (j + t[i] <= T) {
        f[i][j + t[i]] -= fac * tmp[j];
        f[i + 1][j + t[i]] += fac * tmp[j];
      }
    }
  }
  double ans = 0;
  for (int i = 1; i <= n + 1; i++) ans += (i - 1) * f[i][T];
  printf("%.10lf", ans);
  return 0;
}
