思考许久。。。才想通无非是取两个长的
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn=1000000;
char input[maxn];
//#define local
int zero[maxn];
int main()
{
#ifdef local
freopen("input.txt","r",stdin);
#endif
memset(zero,0,sizeof(zero));
int n,k=0,tmp=0;
scanf("%d",&n);
getchar();
for(int i=0;i<n;++i){
input[i]=getchar();
if(input[i]!='0'){
if(tmp>0){
zero[k++]=tmp;
tmp=0;
}
}
else ++tmp;
}
if(tmp>0)zero[k++]=tmp;
sort(zero,zero+k);
printf("%d\n",zero[k-2]+zero[k-1]);
return 0;
}