#include <bits/stdc++.h>
using namespace std;
const int maxn = 5500;
int n, T;
double dp[maxn][maxn];
int t[maxn];
double p[maxn];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", p + i, t + i);
    p[i] /= 100.;
  }
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double P = p[i], VP = 1 - p[i], VPN = pow(VP, t[i]);
    double temp = 0;
    for (int j = 0; j <= T; j++) {
      if (j - 1 >= 0) temp += dp[i - 1][j - 1];
      if (j - t[i] - 1 >= 0) temp -= dp[i - 1][j - t[i] - 1] * VPN;
      dp[i][j] += temp * P;
      if (j - t[i] >= 0) dp[i][j] += dp[i - 1][j - t[i]] * VPN;
      temp = temp * VP;
      ans += dp[i][j];
    }
  }
  printf("%.11lf\n", ans);
  return 0;
}
