#include <bits/stdc++.h>
using namespace std;
const int N = 500500;
int n, tt;
double f[N], ff[N], pw[N];
int main() {
  scanf("%d%d", &n, &tt);
  f[0] = 1;
  double ans = 0;
  for (int i = 0; i < n; i++) {
    int p, t;
    scanf("%d%d", &p, &t);
    double pp = (100 - p) * 1.0 / 100;
    pw[0] = 1;
    for (int i = 1; i <= tt; i++) {
      pw[i] = pw[i - 1] * pp;
      if (pw[i] < 1e-15) pw[i] = 0;
    }
    double sum = 0;
    for (int j = 0; j <= tt; j++) {
      ff[j] = sum * (1 - pp);
      if (j - t >= 0) ff[j] += f[j - t] * pw[t - 1];
      sum = sum * pp + f[j];
      if (j - t + 1 >= 0) sum -= f[j - t + 1] * pw[t - 1];
    }
    for (int j = 0; j <= tt; j++) {
      if (j + t > tt) {
        ans += f[j] * pw[tt - j] * i;
      }
    }
    for (int j = 0; j <= tt; j++) f[j] = ff[j];
  }
  for (int i = 0; i <= tt; i++) ans += f[i] * n;
  printf("%.10lf\n", ans);
}
