#include<bits/stdc++.h>
using namespace std;
int f[200010];
int off(100005);
int main(){
    freopen("pair.in","r",stdin);
    freopen("pair.out","w",stdout);
    int n;
    cin>>n;
    int psum=0;
    int ans=-1;
    for(int i=1;i<=n;i++){
        int a;
        cin>>a;
        psum+=a*2-1;
        if(psum==0) ans=i;
        else if(f[psum+off]==0) f[psum+off]=i;
        else ans=max(ans,i-f[psum+off]);
    }
    cout<<ans;
    return 0;
}