use proconio::input;

fn main(){
    input!{
        n: u64,
        x: u64,
        mut a: [u64; n],
    };

    let mut result = 0;
    for i in 0..=((n-2) as usize) {
        if a[i] + a[i+1] > x {
            let dif = a[i] + a[i+1] - x;
            if dif > a[i+1] {
                a[i] -= dif - a[i+1];
                a[i+1] = 0;
            } else {
                a[i+1] -= dif;
            }
            result += dif;
        }
    }

    println!("{}", result);
}