题目传送门
看出规律，再二分即可
代码：
#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
int main(){
LL n;
scanf("%lld",&n);
int l=0,r=1e9,node;
while(l<r){
int mid=(l+r)>>1;
if(1LL*mid*mid<=n) l=mid+1,node=mid;
else r=mid-1;
}
printf("%d\n",node);
}
#include<bits/std
