#include<bits/stdc++.h>

int main() { int n, x; cin >> n >> x; vector a(n + 1); for (int i = 1; i <= n; i++) { cin >> a[i]; }

long long ans = 0;
for (int i = n - 1; i >= 1; i--) {
    if (a[i] + a[i + 1] > x) {
        long long need = a[i] + a[i + 1] - x;
        if (a[i + 1] >= need) {
            a[i + 1] -= need;
        } else {
            need -= a[i + 1];
            a[i + 1] = 0;
            a[i] -= need;
        }
        ans += need;
    }
}

cout << ans << endl;

return 0;

}