#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:66777216")
using namespace std;
const double eps = 1e-9;
const int CCC = 55;
const double pi = acos(-1.0);
const long long INF = (long long)2e9 + 1;
const long long LINF = (long long)8e18;
const long long inf = (long long)2e9 + 1;
const long long linf = (long long)8e18;
const long long MM = (long long)1e9 + 7;
int solve();
void gen();
int main() {
  solve();
  return 0;
}
double dp[5007][5007];
int solve() {
  int n, T, t;
  cin >> n >> T;
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 0; i < (int)n; i++) {
    double p;
    cin >> p >> t;
    p /= 100;
    double pw = pow(1 - p, t - 1), cur = 0;
    for (int j = 1; j <= T; j++) {
      cur *= 1 - p;
      cur += dp[i][j - 1] * p;
      if (j >= t) cur -= dp[i][j - t] * p * pw;
      dp[i + 1][j] = cur;
      if (j >= t) dp[i + 1][j] += dp[i][j - t] * pw;
      ans += dp[i + 1][j];
    }
  }
  printf("%.10f", ans);
  return 0;
}
