CatThep

#include <bits/stdc++.h>

using namespace std;

int n, len, f[102][102], a[102];

int cut(int l, int r) {
    if (l+1 == r) return 0;
    if (f[l][r] != -1) return(f[l][r]);

    int res = 1003;
    for (int i=l+1; i<r; ++i)
        res = min(res, cut(l, i) + cut(i, r) + a[r] - a[l]);
    f[l][r] = res;
    return(res);
}

int main() {
    freopen("CatThep.inp", "r", stdin);

    scanf("%d%d", &len, &n);
    for (int i=1; i<=n; ++i) scanf("%d", &a[i]);
    a[0] = 0; a[n+1] = len;
    memset(f, -1, sizeof(f));

    printf("%d", cut(0, n+1));

    return 0;
}