#include <bits/stdc++.h>
using namespace std;
const int maxn = 5050;
int n, m, cur, t;
double p, dp[2][maxn], ans;
int main() {
  scanf("%d%d", &n, &m);
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; i++) {
    cur ^= 1;
    memset(dp[cur], 0, sizeof(dp[cur]));
    scanf("%lf%d", &p, &t);
    p /= 100;
    double tmp = 0;
    for (int j = i; j <= m; j++) {
      tmp *= (1.0 - p);
      tmp += dp[cur ^ 1][j - 1];
      if (j - t - 1 >= 0) tmp -= dp[cur ^ 1][j - t - 1] * pow(1 - p, t);
      dp[cur][j] += tmp * p;
      if (j - t >= 0) dp[cur][j] += dp[cur ^ 1][j - t] * pow(1 - p, t);
      ans += dp[cur][j];
    }
  }
  printf("%.6lf", ans);
  return 0;
}
