#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5000 + 10;
int n, T;
double p[MAXN];
int t[MAXN];
double dp[MAXN][MAXN];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; ++i) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] *= 0.01;
  }
  double ans = 0.0;
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; ++i) {
    double sum = 0.0;
    double npn = pow(1.0 - p[i], t[i]);
    for (int j = 1; j <= T; ++j) {
      sum += dp[i - 1][j - 1];
      if (j > t[i]) {
        sum -= dp[i - 1][j - t[i] - 1] * npn;
      }
      dp[i][j] += sum * p[i];
      if (j >= t[i]) {
        dp[i][j] += dp[i - 1][j - t[i]] * npn;
      }
      sum *= 1.0 - p[i];
      ans += dp[i][j];
    }
  }
  printf("%.8f\n", ans);
  return 0;
}
