#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fll;
const int MAXT = 5010;
double prob[2][MAXT];
double total[MAXT];
int main() {
  prob[0][0] = 1;
  int n, T;
  scanf("%d%d", &n, &T);
  int cur = 0, nxt = 1;
  for (int song = 0; song < n; ++song) {
    double pi;
    int ti;
    scanf("%lf%d", &pi, &ti);
    pi /= 100;
    double acc = 0;
    double tot = 0;
    double pow = 1;
    for (int a = 1; a < ti; ++a) pow *= (1 - pi);
    for (int t = 0; t <= T; ++t) {
      if (t == 0) {
        prob[nxt][t] = 0;
        continue;
      }
      acc = (1 - pi) * acc + prob[cur][t - 1];
      if (t >= ti) acc -= pow * prob[cur][t - ti];
      prob[nxt][t] = acc * pi;
      if (t >= ti) prob[nxt][t] += pow * prob[cur][t - ti];
      tot += prob[nxt][t];
    }
    total[song + 1] = tot;
    cur ^= 1;
    nxt ^= 1;
  }
  double ans = 0;
  for (int song = 1; song <= n; ++song) {
    if (song == n)
      ans += total[song] * n;
    else
      ans += (total[song] - total[song + 1]) * song;
  }
  printf("%f\n", ans);
  return 0;
}
