#include <bits/stdc++.h>
using namespace std;
int n, m;
double ans, p1;
double f[5005][5005];
double p[5005], tmp[5005];
int t[5005];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) {
    int w;
    scanf("%d", &w);
    p[i] = w / 100.0;
    scanf("%d", &t[i]);
  }
  f[1][0] = 1;
  p[n + 1] = 0;
  t[n + 1] = 5000;
  for (int i = 1; i <= n + 1; i++) {
    p1 = pow(1 - p[i], t[i]);
    for (int j = 0; j <= m; j++) tmp[j] = f[i][j];
    for (int j = 0; j <= m; j++) {
      f[i][j + 1] += f[i][j] * (1 - p[i]);
      f[i + 1][j + 1] += f[i][j] * p[i];
      if (j + t[i] <= m) {
        f[i][j + t[i]] -= tmp[j] * p1;
        f[i + 1][j + t[i]] += tmp[j] * p1;
      }
    }
  }
  for (int i = 1; i <= n + 1; i++) ans += f[i][m] * (i - 1);
  printf("%.10lf", ans);
}
