#include<algorithm>
#include<complex>
#include<ctype.h>
#include<iomanip>
#include<iostream>
#include<fstream>
#include<map>
#include<math.h>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<stdio.h>
#include<string>
#include<string>
#include<vector>

using namespace std;
typedef long long ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

template < typename T >
void vprint(T &V){
	for(auto v : V){
    	cout << v << " ";
	}
	cout << endl;
}

ll N, K;

bool can_beat(ll damage){
    ll rest_HP = N - damage;
    if(rest_HP<=0){
        return true;
    }

    if(rest_HP%K==0){
        ll n = rest_HP/K;
        if(n<damage){
            return true;
        }else{
            return false;
        }
    }else{
        ll n = rest_HP / K;
        if(n<damage){
            return true;
        }else{
            return false;
        }
    }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    cin >> N >> K;

    if(N<=K){
        p(0);
        return 0;
    }

    ll left = 0;
    ll right = inf;

    while(left+1!=right){
        // p2(left, right);
        ll center = (left+right)/2;    
        if(can_beat(center)){
            right = center;
        }else{
            left = center;
        }
    }
    p(right);
    
    return 0;
}