#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:256000000")
using namespace std;
const int maxN = 5100;
const double eps = 1e-15;
int n, m;
int b[maxN], a[maxN];
double p[maxN];
double d[2][maxN];
double dp[110][maxN];
inline double getValue(int u, int n) {
  if (n < 0) {
    return 0.0;
  }
  return d[u][n];
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; ++i) {
    scanf("%d%d", &b[i], &a[i]);
    p[i] = (double)(b[i]) / 100.0;
  }
  for (int i = 0; i <= 100; ++i) {
    double value = 1.0;
    dp[i][0] = value;
    double q = (double)(i) / 100.0;
    for (int j = 1; j < maxN; ++j) {
      dp[i][j] = dp[i][j - 1] * (1.0 - q);
      if (dp[i][j] < eps) {
        dp[i][j] = 0.0;
        break;
      }
    }
  }
  int u, v;
  u = 0, v = 1;
  for (int i = 0; i <= m; ++i) {
    d[u][i] = 0.0;
  }
  d[u][0] = 1.0;
  double res = 0.0;
  for (int i = 0; i <= n; ++i, swap(u, v)) {
    if (i == n) {
      for (int j = 0; j <= m; ++j) {
        if (d[u][j] < eps) {
          continue;
        }
        res += (double)(n)*d[u][j];
      }
      break;
    }
    for (int j = 0; j <= m; ++j) {
      if (d[u][j] < eps || a[i] <= m - j) {
        continue;
      }
      res += (double)(i)*d[u][j] * dp[b[i]][m - j];
    }
    for (int j = 0; j <= m; ++j) {
      d[v][j] = 0.0;
    }
    if (a[i] == 1) {
      for (int j = 1; j <= m; ++j) {
        d[v][j] = d[u][j - 1];
      }
      continue;
    }
    d[v][1] = d[u][0] * p[i];
    if (d[v][1] < eps) {
      d[v][1] = 0.0;
    }
    double q = 1.0;
    for (int j = 1; j <= a[i] - 2; ++j) {
      q *= (1.0 - p[i]);
      if (q < eps) {
        q = 0.0;
        break;
      }
    }
    double x = p[i] * q;
    double y = q * (1.0 - p[i]);
    for (int j = 2; j <= m; ++j) {
      d[v][j] = d[v][j - 1] - getValue(u, j - a[i] - 1) * y -
                getValue(u, j - a[i]) * x;
      d[v][j] *= (1.0 - p[i]);
      d[v][j] += getValue(u, j - a[i]) * y;
      d[v][j] += d[u][j - 1] * p[i];
      if (d[v][j] < eps) {
        d[v][j] = 0.0;
      }
    }
  }
  printf("%.10lf\n", res);
  return 0;
}
