#include <iostream>
#include <fstream>

using namespace std;

ifstream in ("zombie.in");
ofstream out ("zombie.out");

int V[1000010];

int main()
{
    int D, N, K, i, x;

    in >> D >> N >> K;

    for (i = 1; i <= N; i ++)
        in >> V[i];
    int poz_innt;
    int zombii=1;
    int first = 1;
    poz_innt = D;
    int show = 0;
    for (i = 2; i <= N; i ++)
    {
        if(poz_innt - V[i] + V[first]  >= 0)
        {
            ++zombii;
            poz_innt += V[first]-V[i];
        }
        else
        {
            if(zombii < K)
            {
                show += zombii;
            }
            else
            {
                show += K;
            }
            zombii^=zombii;
            first = i;
        }
    }

    out << show;

    return 0;
}