#include <bits/stdc++.h>
#include <unordered_map>
#include <utility>

#define pb push_back
#define mp make_pair
#define F first
#define S second
#define ll long long int

#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define REP(i,n) for(ll i=0;i<(n);i++)
#define FOR(i,a,b) for(ll i=(a);i<=(b);i++)
#define FORD(i,a,b) for(ll i=(a);i>=(b);i--)

#define all(v) (v).begin(),(v).end()

inline bool EQ(double a, double b) { return fabs(a-b) < 1e-9; }
const ll INF = 1<<29;
inline ll two(ll n) { return 1 << n; }
inline ll test(ll n, ll b) { return (n>>b)&1; }
inline void setBit(ll & n, ll b) { n |= two(b); }
inline void unsetBit(ll & n, ll b) { n &= ~two(b); }
inline ll last_bit(ll n) { return n & (-n); }
inline ll ones(ll n) { ll res = 0; while(n && ++res) n-=n&(-n); return res; }

inline int parent(int x){return floor((x-1)/2);};
inline int left(int x) {return 2*x+1;};
inline int right(int x){return 2*x+2;};

inline bool sortDown(ll x,ll y){return x>y;}
inline bool sortPairSecond( std::pair< ll,ll > p1, std::pair< ll,ll > p2){ return p1.S>p2.S;}
inline bool sortDownByLen( std::pair< ll,ll > p1, std::pair< ll,ll > p2 ){ return p1.S-p1.F > p2.S-p2.F;}


#define MOD 1000000007
using namespace std;
/////////////////////////////////////////////////////////////////////



int main()
{
    std::ios::sync_with_stdio(false);

    ll n,m; cin>>n>>m;

    if(m>=n){
        cout<<n<<endl;
    }
    else{
        ll hi,lo;
        hi=n;
        lo=m;
        bool flag=false;

        // DEBUG(n-m);

        while(hi-lo>1){
            ll mid=(hi+lo)/2;

            if((n-m-((mid*(mid+1))/2)) >0){
                lo=mid;
            }
            else if((n-m-((mid*(mid+1))/2))==0){
                flag=true;
                hi=mid;
                break;
            }
            else{
                hi=mid;
            }
        }

        if(flag){
            cout<<m+hi<<endl;
            return 0;
        }

        // DEBUG(hi);
        // DEBUG(lo);

        // DEBUG((lo*(lo+1)/2));

        if((n-m-((lo*(lo+1))/2))==0){
            // cout<<"hi"<<endl;
            cout<<m+lo<<endl;
        }
        else{
            cout<<m+hi<<endl;
        }
    }

}