1195B- Sport Mafia.cpp

#include<bits/stdc++.h>
using namespace std;

//{
#define si(a) scanf("%d",&a)
#define sii(a,b) scanf("%d %d",&a,&b);
#define siii(a,b,c) scanf("%d %d %d",&a,&b,&c);

#define sl(a) scanf("%lld",&a)
#define sll(a,b) scanf("%lld %lld",&a,&b);
#define slll(a,b,c) scanf("%lld %lld %lld",&a,&b,&c);

#define outi(a) printf("%d\n",a)
#define outii(a,b) printf("%d %d\n",a,b)
#define outis(a) printf(" %d",a)

#define outl(a) printf("%lld\n",a)
#define outll(a,b) printf("%lld %lld\n",a,b)
#define outls(a) printf(" %lld",a)

#define cel(n,k) ((n-1)/k+1)
#define sets(a) memset(a, -1, sizeof(a))
#define clr(a) memset(a, 0, sizeof(a))
#define fr(n) for(int i=0;i<n;i++)
#define fr1(n) for(int i=1;i<=n;i++)
#define frj(n) for(int j=0;j<n;j++)
#define frj1(n) for(int j=1;j<=n;j++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define mp make_pair
#define ff first
#define ss second
#define INF 10000007
#define fastIO() ios_base::sync_with_stdio(false); cin.tie(NULL);

typedef long long i64;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;
//}

const int maxn= 1e5+5;

i64 n, k, ans;

int can(i64 q){
    i64 op1= n-q;

    i64 total= (op1*(op1+1))/2;
    i64 rem= total- q;

    if(k==rem)
        return 0;
    else if(rem>k)
        return 1;
    else
        return -1;

}

int main(){
    sll(n,k);

    i64 lo= 0, hi= n;


    while(lo<=hi){
        i64 mid= (lo+hi)/2;

        if(can(mid)==0){
            outl(mid);
            return 0;
        }
        else if(can(mid)==1)
            lo= mid+1;
        else
            hi= mid-1;
    }


}