#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
typedef long long ll;
using P = pair<int,int>;
#define F first
#define S second
template<class T> inline bool chmax(T& a, T b){ if(a<b){ a=b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b){ if(a>b){ a=b; return 1; } return 0; }

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(m);
  rep(i, m) cin >> a[i];
  a.push_back(0);
  a.push_back(n+1);
  sort(all(a));
  int b;
  b = n;
  rep(i, m+1) {
    if (a[i+1] - a[i] != 1) {
      chmin(b, a[i+1] - a[i] - 1);
    }
  }
  int ans = 0;
  rep(i, m+1) {
    if (a[i+1] - a[i] != 1) {
      ans += (a[i+1] - a[i] - 1 + b - 1) / b;
    }
  }
  cout << ans << endl;
}

#include <bits/stdc++.h>
#define gc() getchar()
using namespace std;
typedef long long ll;

template <typename T> void rd(T &x){
	ll f=1;x=0;char c=gc();
	for(;!isdigit(c);c=gc())if(c=='-')f=-1;
	for(;isdigit(c);c=gc())x=(x<<1)+(x<<3)+(c^48);
	x*=f;
}

int main(){
	int a,b;
	rd(a),rd(b);
	printf("%g\n",1.0*a*b/100);
	return 0;
}
