#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:1024000000,1024000000")
using namespace std;
double dp[5010], f[5010];
int main() {
  int T, i, j, k, ca = 0, n, m;
  while (~scanf("%d%d", &n, &T)) {
    for (i = 0; i <= T; i++) dp[i] = 0;
    dp[0] = 1;
    double ans = 0;
    for (i = 0; i < n; i++) {
      int p1, t;
      scanf("%d%d", &p1, &t);
      double p = 1. * p1 / 100, q = 1;
      for (j = 1; j < t; j++) q *= (1 - p);
      f[0] = dp[0];
      for (j = 1; j <= T; j++) f[j] = f[j - 1] * (1 - p) + dp[j];
      for (j = T; j >= 1; j--) {
        double c = 0;
        if (j >= t) c = f[j - t];
        dp[j] = (f[j - 1] - c * q) * p;
        if (j >= t) dp[j] += q * dp[j - t];
      }
      dp[0] = 0;
      for (j = 1; j <= T; j++) ans += dp[j];
    }
    printf("%lf\n", ans);
  }
}
