#include <bits/stdc++.h>
//#include "robot.h"
using namespace std;
#define fi first
#define se second
#define pb push_back
const int nax = 5e5+5;
vector<int> tab[nax];
int main()
{
int n;
cin>>n;
int q;
cin>>q;
while(q--){
int c;
cin>>c;
tab[abs(c)].push_back((c>0 ? 1 : -1));
}
int ans=0;
for (int i = 1; i <= n; ++i)
{
int lst=0;
//if(tab[i].size()) cout <<i<<" "<<tab[i].size()<<endl;
ans=max(ans,(int)tab[i].size()-1);
/*for(int j = 0; j<tab[i].size() ; j++){
if(tab[i][j]>0) lst++;
else{
if(lst) lst--;
while(j<tab[i].size()&&tab[i][j]<0){
j++;
}
j--;
}
ans=max(ans,lst);
}*/
}
cout <<ans<<endl;
}
