import std.stdio, std.string, std.conv, std.algorithm, std.numeric;
import std.range, std.array, std.math, std.typecons, std.container, core.bitop;

void main() {
    int n, p;
    scan(n, p);
    auto h = readln.split.to!(int[]);

    auto dpr = new long[](n);
    auto dpl = new long[](n);

    foreach (i ; 1 .. n) {
        if (i == 1) {
            dpr[i] = min(min(dpr[i-1], dpl[i-1]) + p, dpr[i-1] + max(h[i] - h[i-1], 0));
            dpl[i] = min(dpr[i-1], dpl[i-1]) + p;
        }
        else {
            dpr[i] = min(min(dpr[i-1], dpl[i-1]) + p, dpr[i-1] + max(h[i] - h[i-1], 0));
            dpl[i] = min(min(dpr[i-1], dpl[i-1]) + p, dpl[i-1] + max(h[i-1] - h[i], 0));
        }
    }

    writeln(min(dpr[n-1], dpl[n-1]));
}



void scan(T...)(ref T args) {
    string[] line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}



void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}