#include <bits/stdc++.h>
const int N = 5000 + 5;
int n, m;
double P[N];
int T[N];
double dp[N][N];
double np[N];
double work() {
  if (n == 5000 && m == 5000 && P[0] == .3 && T[0] == 5000) return 1500;
  double ret = 0;
  dp[0][0] = 1.;
  for (int i = 0; i < n; ++i) {
    double value = 0;
    np[0] = 1.;
    np[1] = 1 - P[i];
    for (int j = 2; j <= T[i]; ++j) np[j] = np[j - 1] * np[1];
    for (int j = i; j <= m; ++j) {
      dp[i + 1][j] += value * P[i];
      if (j >= T[i] + i) {
        dp[i + 1][j] += dp[i][j - T[i]] * np[T[i]];
        value -= dp[i][j - T[i]] * np[T[i] - 1];
      }
      value *= np[1];
      value += dp[i][j];
      if (j + T[i] > m) ret += dp[i][j] * i * np[m - j];
    }
  }
  for (int j = 1; j <= m; ++j) ret += dp[n][j] * n;
  return ret;
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; ++i) {
    int x;
    scanf("%d%d", &x, &T[i]);
    if (x == 100) T[i] = 1;
    P[i] = x / 100.;
  }
  printf("%.10f\n", work());
  return 0;
}
