#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5003;
double f[MAXN], s[MAXN], p[MAXN], ans = 0.0, product, tmp;
int n, T, t[MAXN], x;
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 0; i < n; ++i) {
    scanf("%d%d", &x, &t[i]);
    p[i] = (100.0 - x) / 100.0;
  }
  f[0] = 1.0;
  for (int i = 0; i < n; ++i) {
    product = 1.0;
    for (int j = 1; j < t[i]; ++j) product *= p[i];
    s[0] = f[0];
    for (int j = 1; j <= T; ++j) s[j] = s[j - 1] * p[i] + f[j];
    for (int j = T; j; --j) {
      tmp = s[j - 1] - (j >= t[i] ? s[j - t[i]] * product : 0.0);
      f[j] = tmp * (1.0 - p[i]);
      if (j >= t[i]) f[j] += product * f[j - t[i]];
    }
    for (int j = 1; j <= T; ++j) ans += f[j];
    f[0] = 0.0;
  }
  printf("%.9lf\n", ans);
  return 0;
}
