#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
using ll = long long int;

ll dp[200010][2];
const ll INF = 1LL << 60;
int main() {
    ll N, P; scanf("%lld%lld", &N, &P);
    vector<ll> H(N);
    for(int i=0; i<N; i++) scanf("%lld", &H[i]);
    
    fill(dp[0], dp[N+1], INF);
    dp[0][0] = 0;

    for(int i=0; i+1<N; i++) {
        for(int x=0; x<2; x++) {
            // fprintf(stderr, "dp[%d][%d] = %lld\n", i+1, x, dp[i][x]);
            for(int y=0; y<2; y++) {
                ll add = P;
                if(x == y and y == 0) add = min(add, max(H[i+1] - H[i], 0LL));
                if(x == y and y == 1) add = min(add, max(H[i] - H[i+1], 0LL));

                dp[i+1][y] = min(dp[i+1][y], dp[i][x] + add);
            }
        }
        // fprintf(stderr, "\n");
    }

    printf("%lld\n", min(dp[N-1][0], dp[N-1][1]));
    return 0;
}