#include <bits/stdc++.h>

using i32 = std::int32_t;
using u32 = std::uint32_t;
using i64 = std::int64_t;
using u64 = std::uint64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

class rep {
    struct Iter {
        usize itr;
        constexpr Iter(const usize pos) noexcept: itr(pos) { }
        constexpr void operator ++ () noexcept { ++itr; }
        constexpr bool operator != (const Iter& other) const noexcept { return itr != other.itr; }
        constexpr usize operator * () const noexcept { return itr; }
    };
    const Iter first, last;
public:
    explicit constexpr rep(const usize first, const usize last) noexcept: first(first), last(std::max(first, last)) { }
    constexpr Iter begin() const noexcept { return first; }
    constexpr Iter end() const noexcept { return last; }
};

template <class T>
using Vec = std::vector<T>;

void G_main() {
    u64 N;
    std::cin >> N;
    u64 ok = N, ng = 0;
    while (ok - ng > 1) {
        const auto md = (ok + ng) / 2;
        if (md * (md + 1) >= 2 * N) {
            ok = md;
        }
        else {
            ng = md;
        }
    }
    std::cout << ok << '\n';
    return;
}

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    G_main(); 
    return 0;
}