#include <bits/stdc++.h>
using namespace std;
int n, T;
double dp[5001][5001];
int p[5001], t[5001];
double quickpow(double x, int y) {
  double res = 1;
  while (y) {
    if (y & 1) res *= x;
    x *= x;
    y >>= 1;
  }
  return res;
}
int main() {
  cin >> n >> T;
  dp[0][0] = 1;
  for (int i = 0; i < n; i++) scanf("%d%d", &p[i], &t[i]);
  double ans = 0;
  for (int i = 0; i < n; i++) {
    double pp = p[i] * 0.01;
    double now = 0;
    double r = quickpow(1 - pp, t[i] - 1) * pp;
    double r2 = quickpow(1 - pp, t[i] - 1);
    for (int j = 0; j < T; j++) {
      now *= (1 - pp);
      now += dp[i][j] * pp;
      if (j + 1 >= t[i]) {
        now -= dp[i][j + 1 - t[i]] * r;
        dp[i + 1][j + 1] = now + dp[i][j + 1 - t[i]] * r2;
      } else {
        dp[i + 1][j + 1] = now;
      }
    }
    for (int j = 0; j <= T; j++) ans += dp[i + 1][j];
  }
  printf("%.12f\n", ans);
  return 0;
}
