#include<bits/stdc++.h>
using namespace std;

/*#include<atcoder/all>
using namespace atcoder;*/

typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pi;
typedef vector<pi> pii;
#define all(x) x.begin(),x.end()
#define sz(x) (int)(x).size()
#define pb push_back
#define mk make_pair
#define en '\n'

void solve(){
    float a,b;
    cin >> a >> b;
    cout << (a*b)/100 << en;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    //freopen("div7.in","r",stdin);
    //freopen("div7.out","w",stdout);

    int t = 1;
    //cin >> t;
    while(t--) {
        solve();
    }
    return 0;
}   

#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define ENDL '\n'
#define sz(s) int(s.size())
#define deb(x) cout << #x": " << (x) << endl;
#define all(s) begin(s), end(s)
#define fore(i,a,b) for(int i = (a), ThxMK = (b); i < ThxMK; ++i)
#define _ ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

using namespace std;

typedef long double ld;
typedef long long lli;
typedef pair<lli,lli> ii;
typedef vector<lli> vi;

lli f(lli u, lli v) {
  if(u == 0) return 0;
  if(u % v) return (v + u - (u % v)) / v;
  return u / v;
}

int main(){ _
  lli n, m;
  cin >> n >> m;
  if(m == 0) {
    cout << 1 << ENDL;
    return 0;
  }
  vi v(m); fore(i, 0, m) cin >> v[i];
  sort(all(v));
  lli prev = 0;
  lli mn = n;
  for(auto it : v) {
    lli aux = (it - prev - 1);
    prev = it;
    if(aux == 0) continue;
    mn = min(mn, aux);
  }
  lli aux = n - prev;
  if(aux != 0) mn = min(mn, aux);
  prev = 0;
  lli ans = 0;
  for(auto it : v) {
    lli aux = (it - prev - 1);
    prev = it;
    ans += f(aux, mn);
  }
  aux = n - prev;
  ans += f(aux, mn);
  cout << ans << ENDL;
  return 0;
}
