cf 689 C(二分)

                链接：http://codeforces.com/problemset/problem/689/C

#include <bits/stdc++.h>
using namespace std;
#define ll long long

ll get(ll n)
{
    ll ans=0;
    for(ll k=2;k*k*k<=n;k++)
        ans+=n/(k*k*k);
    return ans;
}

int main()
{
    ll m;
    while(~scanf("%lld",&m))
    {
        ll l=1,r=1e16;
        while(l<=r)
        {
            ll mid=(l+r)/2;
            if(get(mid)>=m)r=mid-1;
            else l=mid+1;
        }
        if(get(l)==m)printf("%lld\n",l);
        else printf("-1\n");
    }

    return 0;
}