#include <bits/stdc++.h>
using namespace std;
const int maxn = 5001;
int n, T, tt;
double p[maxn];
int t[maxn];
double f[maxn][maxn];
double ans = 0;
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double tp = 1, temp = 0;
    for (int j = 1; j <= T; j++) {
      temp = temp * (1 - p[i]) + f[i - 1][j - 1] * p[i];
      if (j >= t[i]) {
        temp -= f[i - 1][j - t[i]] * p[i] * tp;
        f[i][j] += f[i - 1][j - t[i]] * tp;
      } else
        tp *= 1 - p[i];
      f[i][j] += temp;
    }
    tp = 1;
    for (int j = T; j > 0; j--, tp *= 1 - p[i + 1]) {
      if (i == n)
        ans += i * f[i][j];
      else if (j + t[i + 1] > T)
        ans += i * f[i][j] * tp;
      else
        break;
    }
  }
  printf("%.8f\n", ans);
  return 0;
}
