#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5050;
int n, T, t[MAXN];
double dp[2][MAXN], p[MAXN];
int P[MAXN];
double factor[101][MAXN];
double *f[2];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &P[i], &t[i]);
    p[i] = P[i] / 100.0;
  }
  double res = 0;
  f[0] = dp[0];
  f[1] = dp[1];
  for (int k = 0; k <= T; k++) f[0][k] = 1;
  for (int i = 0; i <= 100; i++) {
    factor[i][0] = 1;
    double K = 1.0 - i / 100.0;
    for (int k = 1; k <= T; k++) {
      factor[i][k] = factor[i][k - 1] * K;
    }
  }
  for (int i = 1; i <= n; i++) {
    double delta = 0;
    double K = 1 - p[i];
    f[1][0] = 0;
    for (int j = 1; j < t[i]; j++) {
      delta = delta * K + f[0][j - 1] * p[i];
      f[1][j] = delta;
    }
    for (int j = t[i]; j <= T; j++) {
      double L = factor[P[i]][t[i] - 1] * f[0][j - t[i]];
      delta = delta * K + (f[0][j - 1] - L) * p[i];
      f[1][j] = delta + L;
    }
    res += (i - 1) * (f[0][T] - f[1][T]);
    swap(f[0], f[1]);
  }
  res += n * f[0][T];
  printf("%.6f\n", res);
}
