757 B | 757 chars
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef vector <ll> llv1;
typedef unsigned int uint;
typedef vector <ull> ullv1;
typedef vector <vector <ull>> ullv2;
ll N,s=1,e=3000000000ll,mid;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N;
while(s<=e) {
mid = (s+e) / 2;
if(mid % 3 ==0 || mid % 5 ==0) {
s-=2;
e+=7;
continue;
}
ll count = mid/3 + mid/5 - mid/15;
if(mid - count == N) {
cout << mid;
return 0;
}
if(mid - count > N) e = mid -1;
else s = mid +1;
}
}