#include <bits/stdc++.h>
using namespace std;
int T, n, t[5005];
double ans, p[5005], g[5005], f[5005][5005];
double fast_pow(double a, int p) {
  double ans = 1.0;
  for (; p; p >>= 1, a *= a)
    if (p & 1) ans *= a;
  return ans;
}
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; ++i) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100.0;
  }
  f[1][1] = 1;
  p[n + 1] = 0;
  t[n + 1] = 5000;
  for (int i = 1; i <= n + 1; ++i) {
    double P = fast_pow(1 - p[i], t[i]);
    for (int j = 1; j <= T + 1; ++j) g[j] = f[i][j];
    for (int j = 1; j <= T + 1; ++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] <= T + 1) {
        f[i][j + t[i]] -= g[j] * P;
        f[i + 1][j + t[i]] += g[j] * P;
      }
    }
  }
  for (int i = 1; i <= n + 1; ++i) ans += f[i][T + 1] * (i - 1);
  printf("%.9lf\n", ans);
}
