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

int main(void) {
    ll n, m, k;
    scanf("%lld%lld%lld", &n, &m, &k);

    ll g = n/k, opt = 0;
    while (g >= 0 && g*k + (k-1)*m >= n) {
        ll sz = (n-g*k) / m, rem = (n-g*k) % m;
        // g groups of size k, (m-rem) groups of size sz, and rem groups of size sz+1
        
        ll val = k*g*(g+1)/2;          // g groups of size k causing k+2k+3k+...+gk damage
        for (int i = 0; i < m; ++i) {
            if (i < rem)
                val += (g+i+1)*(sz+1); // group of size sz+1 getting killed in round g+i+1
            else
                val += (g+i+1)*sz;     // group of size sz getting killed in round g+i+1
        }
        opt = max(opt, val);
        --g;
    }
    printf("%lld\n", opt);
}