#include<iostream>
using namespace std;
int main(){
long long broiuchenitsi,index,index2,broyach=1;
cin>>broiuchenitsi;
long long pur[broiuchenitsi],vtor[broiuchenitsi],okonch[broiuchenitsi];
long long detsa[broiuchenitsi],pazitel[broiuchenitsi][broiuchenitsi],broyach2[broiuchenitsi],naigolqmo=0;
for(index=0;index<broiuchenitsi;index++){
cin>>detsa[index];
pur[index]=0;
vtor[index]=0;
okonch[index]=0;
broyach2[index]=0;
}	
for(index=0;index<broiuchenitsi;index++){
	for(index2=0;index2<broiuchenitsi;index2++){
	pazitel[index][index2]=0;
	if(broyach<detsa[index]){
	pazitel[index][index2]=detsa[index]-broyach;
	pur[index]=pazitel[index][index2];	
	}else{
	pazitel[index][index2]=broyach-detsa[index];
	vtor[index]=pazitel[index][index2];	
	}
	broyach++;
	if(detsa[index]+1<broiuchenitsi+1){
	detsa[index]++;
	}else{
	detsa[index]=1;	
	}
	}
}
for(index=0;index<broiuchenitsi;index++){
	if(pur[index]>vtor[index]){
	okonch[index]=vtor[index];	
	}else{
	okonch[index]=pur[index];	
	}
}
for(index=0;index<broiuchenitsi;index++){
	for(index2=0;index2<broiuchenitsi;index2++){
	if(okonch[index]==pazitel[index][index2]){
	broyach2[index]++;
	}
		}
}
naigolqmo=broyach2[0];
for(index=1;index<broiuchenitsi;index++){
if(naigolqmo<broyach2[index]){
naigolqmo=broyach2[index];	
}
}
cout<<naigolqmo;
return 0;
}
