#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back  
#define all(x) x.begin(), x.end()
#define ins insert
#define F first
#define S second
const int N = 2e5 + 7, mod = 998244353;
void solve(){
	int n, q;
	cin>>n>>q;
	map<int, int>mp;
	int mx = 0;
	for(int i = 1; i <= n; i++){
	    mp[i] = -1e9;
	}
	for(int i = 1; i <= q; i++){
	    int x;
	    cin>>x;
	    if(x > 0){
	        mx = max(mx, mp[x] + 1);
	        mp[x] = mx;
	    }
	    else{
	        mp[x]--;
	    }
	}
	cout<<mx;
}
signed main(){
	ios_base :: sync_with_stdio(false);
	cin.tie(0);
    //freopen("pieaters.in", "r", stdin);
    //freopen("pieaters.out", "w", stdout);
    int t = 1;
    //cin>>t;
    while(t--){
        solve();
    }
}
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