#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int n, v, DP[N][N], result = 1e9 + 7;
main()
{
    cin >> n >> v;

    memset(DP, 0x3f3f3f3f, sizeof(DP));
    DP[1][0] = 0;
    for (int i = 1; i <= n; i++){
        for (int j =0; j<=v;j++){
            for (int l=1;l<=v-j;l++){
                DP[i][j + l] = min( DP[i][j + l], DP[i][j] + l * i );
            }
            if (j > 0)
                DP[i + 1][j - 1] = min( DP[i + 1][j - 1], DP[i][j] );
        }
    }
    for (int j = 0; j <= v; j++)
        result = min( result, DP[n][j] );

    cout << result << endl;
}