//Rahman ve Rahim olan Allah'ın adıyla
#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define ins insert
#define fi first
#define se second
#define int long long
#define mid (st+end)/2
#define spc <<" "<<
#define en <<"\n"
#define amin main
int32_t amin(){
ios_base::sync_with_stdio(false);cin.tie(0);
//freopen("input.txt","r",stdin);freopen("output.txt","w",stdout);
int n,q,a;cin>>n>>q;vector<int>strk(n,0);vector<int>res(n,0);
for(int i=0;i<q;i++){
cin>>a;
if(a<0){
if(strk[abs(a)]!=0){//cout<<"fgh";
res[abs(a)]+=strk[abs(a)]-1;
}strk[abs(a)]=0;//cout<<a<<"\n";
}else{
strk[abs(a)]++;//cout<<"ed"<<abs(a)<<strk[abs(a)]<<"\n";
}
}
for(int i=0;i<n;i++){
if(strk[i]!=0){
res[i]+=strk[i]-1;
}
}int ans=-1;
for(auto it:res){
ans=max(ans,it);
}cout<<ans;
}
