#include <bits/stdc++.h>
using namespace std;
int N, T;
double P;
int TT;
double P2[2][6001];
double ret;
void solve() {
  int i, j, k, l, r, x, y;
  string s;
  cin >> N >> T;
  P2[0][0] = 1;
  double ret = 0;
  for (i = 0; i < N; i++) {
    int cur = i % 2, tar = cur ^ 1;
    cin >> P >> TT;
    if (P == 100) TT = 1;
    if (TT == 1) P = 100;
    P /= 100;
    double pt1 = pow(1 - P, TT - 2) * P;
    double pt0 = pow(1 - P, TT - 1);
    if (pt1 < 1e-13) pt1 = 0;
    if (pt0 < 1e-13) pt0 = 0;
    memset(P2[tar], 0, sizeof(P2[tar]));
    double tt = 0, left = 1;
    for (j = i + 1; j <= T; j++) {
      if (TT == 1) {
        tt = P2[cur][j - 1];
      } else {
        if (j >= (TT + 1) && pt0) tt -= P2[cur][j - (TT + 1)] * pt0;
        if (j >= (TT) && pt1) tt -= P2[cur][j - TT] * pt1;
        tt *= 1 - P;
        if (j >= (TT) && pt0) tt += P2[cur][j - TT] * pt0;
        tt += P2[cur][j - 1] * P;
      }
      ret += tt;
      left -= tt;
      if (tt > 1e-15) P2[tar][j] = tt;
    }
  }
  (void)printf("%.12lf\n", ret);
}
int main(int argc, char** argv) {
  string s;
  int i;
  if (argc == 1) ios::sync_with_stdio(false);
  for (i = 0; i < argc - 1; i++) s += argv[i + 1], s += '\n';
  for (i = 0; i < s.size(); i++) ungetc(s[s.size() - 1 - i], stdin);
  solve();
  return 0;
}
