689C - Mike and Chocolate Thieves - CodeForces Solution

#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define N 100005
using namespace std;
vector<int>adj[N];
int fun(int n){
      int sum = 0;
      for(int r = 2; r<=cbrt(n); r++){
            sum += (n/(r*r*r));
      }
      return sum;
}
int32_t main(){
           int m;
           cin>>m;
           
           int res = -1;
           int low = 1;
           int high = 1e18;
           while(low<=high){
                 int mid = (low+high)/2;
                 if(fun(mid)==m)
                  {
                        res = mid;
                        high = mid-1;
                  }
                  else if(fun(mid) > m){
                        high = mid-1;
                  }
                  else
                        low = mid+1;
           }
           
           cout<<res<<endl;
        }
        
    
   // 1 + 1 + 2 + 4 + 8