零分...大佬求教!

#include<bits/stdc++.h>
using namespace std;
const int N=50005;
int s[N],a[N],n,mx;
int fr[7],ls[7];
int main(){
    cin>>n;
    memset(fr,-1,sizeof(fr));
    memset(ls,-1,sizeof(ls));
    for(int i=1;i<=n;i++){
        cin>>a[i];
        s[i]=(s[i-1]+a[i])%7;
        if(fr[s[i]]==-1) 
            fr[s[i]]==i;
        ls[s[i]]=i;
        
    }
    
    for(int i=1;i<=6;i++){
        if(fr[i]!=-1) mx=max(mx,ls[i]-fr[i]);
    }
    cout<<mx;
    return 0;
}