#include <bits/stdc++.h>
int n, m, F, t[5005];
double p[5005], f[5005][2], pw[5005], w, now;
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) scanf("%lf %d", &p[i], &t[i]), p[i] /= 100;
  for (int i = n; i; i--) {
    w = 1;
    now = 0;
    for (int j = 1; j < t[i]; j++) w *= 1 - p[i];
    for (int j = m - 1; j >= 0; j--) {
      now = (1 - p[i]) * now + p[i] * (1 + f[j + 1][F]);
      if (j + t[i] <= m)
        now -= w * p[i] * (1 + f[j + t[i]][F]),
            f[j][!F] = now + w * (1 + f[j + t[i]][F]);
      else
        f[j][!F] = now;
    }
    F ^= 1;
  }
  printf("%.9lf\n", f[0][F]);
}
