#include <bits/stdc++.h>
#pragma comment(linker, "/stack:225450978")
#pragma GCC optimize("Ofast")
using namespace std;
const long long Mod = 1000000007LL, INF = 1e9, LINF = 1e18;
const long double Pi = 3.141592653589793116, EPS = 1e-9,
                  Gold = ((1 + sqrt(5)) / 2);
long long keymod[] = {1000000007LL, 1000000009LL, 1000000021LL, 1000000033LL};
long long keyCount = sizeof(keymod) / sizeof(long long);
template <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return __builtin_popcountll(s);
}
auto TimeStart = chrono::steady_clock::now();
auto TimeEnd = chrono::steady_clock::now();
void ControlIO(int argc, char* argv[]);
void TimerStart();
void TimerStop();
void Exit();
int n, T;
int p[5001], t[5001];
double afterIntro[5001], maxStocked[5001];
double dp[5001][5001];
void Input() {
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    double Last = 1.0;
    afterIntro[i] = 1.0;
    maxStocked[i] = 1.0;
    for (int x = 1; x < t[i]; x++) {
      afterIntro[i] -= Last * p[i] / 100;
      maxStocked[i] *= (100 - p[i]);
      maxStocked[i] /= 100;
      Last *= (100 - p[i]);
      Last /= 100.0;
    }
  }
}
void Solve() {
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; i++) {
    double Curr = 0.0;
    for (int j = 0; j <= T; j++) {
      if (j - t[i] >= 0) {
        dp[i][j] += dp[i - 1][j - t[i]] * afterIntro[i];
        Curr -= dp[i - 1][j - t[i]] * maxStocked[i];
      }
      dp[i][j] += Curr * p[i] / 100;
      Curr *= (100 - p[i]);
      Curr /= 100;
      if (j < T) Curr += dp[i - 1][j];
    }
    dp[i - 1][T] += Curr;
  }
  double expected = 0;
  for (int i = 1; i <= n; i++) expected += dp[i][T] * i;
  for (int i = 0; i < T; i++) expected += dp[n][i] * n;
  cout << fixed << setprecision(12) << expected;
}
int main(int argc, char* argv[]) {
  ControlIO(argc, argv);
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  Input();
  TimerStart();
  Solve();
  TimerStop();
  return 0;
}
void ControlIO(int argc, char* argv[]) {}
void TimerStart() {}
void TimerStop() {}
void Exit() {
  TimerStop();
  exit(0);
}
