CodeForces 689C【二分】

#include<stdio.h>
typedef long long ll;
ll check(ll n)
{
ll res=0;
for(ll k=2; k*k*k<=n; k++)//k是ll范围  不可犯糊涂
res+=n/(k*k*k);
return res;
}
int main()
{
ll m,res=-1,l=1,r=1e18,mid;
scanf("%I64d",&m);
while(r>=l)
{
mid=(l+r)/2;
ll num= check(mid);
if(num==m)
res=mid;
if(num>=m)
r=mid-1;
else
l=mid+1;
}
printf("%I64d\n",res);
}