#include <bits/stdc++.h>
using namespace std;
double pd[2][5001], pd2[2][5001];
double p[5001], pot[5001];
int tt[5001];
int main(void) {
  int n, t;
  scanf("%d%d", &n, &t);
  for (int i = 0; i < n; i++) {
    int tmp;
    scanf("%d%d", &tmp, &tt[i]);
    p[i] = (double)tmp / 100.0;
    pot[i] = 1;
    for (int j = 1; j < tt[i]; j++) pot[i] *= (1 - p[i]);
  }
  for (int j = 0; j <= t; j++) {
    pd[0][j] = pd2[0][j] = 1;
  }
  double ans = 0;
  int curr = 1;
  for (int i = 0; i < n; i++) {
    int last = 1 - curr;
    pd2[curr][0] = 0;
    for (int j = 1; j <= t; j++) {
      pd2[curr][j] = p[i] * pd[last][j - 1] + (1 - p[i]) * pd2[curr][j - 1];
    }
    pd[curr][0] = 0;
    for (int j = 1; j <= t; j++) {
      pd[curr][j] =
          pd2[curr][j] -
          (j - tt[i] + 1 >= 0 ? pot[i] * pd2[curr][j - tt[i] + 1] : 0) +
          (j - tt[i] >= 0 ? pot[i] * pd[last][j - tt[i]] : 0);
    }
    ans += pd[curr][t];
    curr = last;
  }
  printf("%.10lf\n", ans);
}
