#include <bits/stdc++.h>
using namespace std;
int n, T;
double p[5002];
int t[5002];
double epe[2][5002];
int main() {
  while (cin >> n >> T) {
    for (int i = 1; i <= n; ++i) {
      scanf("%lf%d", p + i, t + i);
    }
    for (int i = 0; i <= 1; ++i) {
      for (int j = 0; j <= T; ++j) {
        epe[i][j] = 0.0;
      }
    }
    int now = 0;
    for (int i = n; i >= 1; --i) {
      now ^= 1;
      double fac = 1.0;
      double pr = p[i] * 0.01;
      for (int j = 1; j < t[i]; ++j) {
        fac *= (1 - pr);
      }
      double tot = 0.0;
      for (int j = 1; j <= T; ++j) {
        tot *= (1 - pr);
        tot += (epe[now ^ 1][j - 1] + 1.0) * pr;
        if (j >= t[i]) {
          tot += (epe[now ^ 1][j - t[i]] + 1.0) * fac * (1 - pr);
        }
        if (j > t[i]) {
          tot -= (epe[now ^ 1][j - t[i] - 1] + 1.0) * fac * (1 - pr);
        }
        epe[now][j] = tot;
      }
    }
    printf("%.10lf\n", epe[now][T]);
  }
  return 0;
}
