#include <bits/stdc++.h>
using namespace std;
int n, m, x, y;
double f[5005][5005], p, g, h, l, tmp, ans;
int main() {
  f[0][0] = 1;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; ++i) {
    f[i][0] = 0;
    for (int j = 1; j <= i - 1; ++j) f[i][j] = 0;
    scanf("%d%d", &x, &y);
    p = x / 100.0;
    g = 1 - p;
    h = pow(g, y - 1);
    l = h * g;
    tmp = 0;
    for (int j = i; j <= m; ++j) {
      if (j < y)
        tmp = tmp * g + p * f[i - 1][j - 1];
      else if (j == y)
        tmp = tmp * g + p * f[i - 1][j - 1] + f[i - 1][0] * l;
      else
        tmp = tmp * g - l * f[i - 1][j - y - 1] + l * f[i - 1][j - y] +
              p * f[i - 1][j - 1];
      f[i][j] = tmp;
      ans += f[i][j];
    }
  }
  printf("%.7f\n", ans);
  return 0;
}
