fn main() {
    let (n, m): (usize, usize) = io::input();
    let ab = (0..n)
        .map(|_| io::input::<(i64, i64)>())
        .collect::<Vec<_>>();
    lg!(n, m, &ab);

    let mut ans = 0;
    let mut dp = vec![0; m + 1];
    for &(a, b) in &ab {
        for i in 1..=m {
            dp[i] += (a * i as i64 + (b - a).max(0)).max(b);
        }
        for i in (1..m).rev() {
            dp[i] = dp[i + 1].max(dp[i]);
        }
        ans = ans.max(dp[1]);
    }
    println!("{ans}");
}
// io {{{
// https://ngtkana.github.io/ac-adapter-rs/io/index.html

#[allow(dead_code)]
mod io {
    use std::cell::Cell;
    use std::io::stdin;
    use std::io::BufRead;
    use std::io::BufReader;
    use std::io::Lines;
    use std::io::Stdin;
    use std::sync::Mutex;
    use std::sync::Once;
    pub fn input<T: ParseLine>() -> T {
        ParseLine::parse_line(&line())
    }
    pub trait ParseLine {
        fn parse_line(s: &str) -> Self;
    }
    macro_rules! impl_parse_line {
        ($($t:ty),*) => {
            $(impl ParseLine for $t {
                fn parse_line(s: &str) -> Self {
                    s.parse().unwrap()
                }
            })*
        };
    }
    impl_parse_line!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize, String, char);
    macro_rules! impl_parse_line_tuple {
        ($($t:ident),*) => {
            impl<$($t: ParseLine),*> ParseLine for ($($t,)*) {
                fn parse_line(s: &str) -> Self {
                    let mut s = s.split_whitespace();
                    ($($t::parse_line(s.next().unwrap()),)*)
                }
            }
        };
    }
    impl_parse_line_tuple!(T0, T1);
    impl_parse_line_tuple!(T0, T1, T2);
    impl_parse_line_tuple!(T0, T1, T2, T3);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4, T5);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4, T5, T6);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4, T5, T6, T7);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4, T5, T6, T7, T8);
    impl_parse_line_tuple!(T0, T1, T2, T3, T4, T5, T6, T7, T8, T9);
    impl<T: ParseLine> ParseLine for Vec<T> {
        fn parse_line(s: &str) -> Self {
            s.split_whitespace().map(T::parse_line).collect()
        }
    }
    static ONCE: Once = Once::new();
    type Server = Mutex<Lines<BufReader<Stdin>>>;
    struct Lazy(Cell<Option<Server>>);
    unsafe impl Sync for Lazy {}
    fn line() -> String {
        static SYNCER: Lazy = Lazy(Cell::new(None));
        ONCE.call_once(|| {
            SYNCER
                .0
                .set(Some(Mutex::new(BufReader::new(stdin()).lines())));
        });
        unsafe {
            (*SYNCER.0.as_ptr())
                .as_ref()
                .unwrap()
                .lock()
                .unwrap()
                .next()
                .unwrap()
                .unwrap()
        }
    }
}
// }}}
// lg {{{
// https://ngtkana.github.io/ac-adapter-rs/lg/index.html

#[allow(dead_code)]
mod lg {
    use std::borrow::Borrow;
    use std::fmt;
    use std::iter::once;
    #[macro_export]
    macro_rules! lg {
        (@contents $head:expr $(, $tail:expr)*) => {{
            $crate::__lg_internal!($head);
            $(
                eprint!(",");
                $crate::__lg_internal!($tail);
            )*
            eprintln!();
        }};
        ($($expr:expr),* $(,)?) => {{
            eprint!("{}\u{276f}", line!());
            $crate::lg!(@contents $($expr),*)
        }};
    }
    #[doc(hidden)]
    #[macro_export]
    macro_rules! __lg_internal {
        ($value:expr) => {{
            match $value {
                head => {
                    eprint!(
                        " {} = {}",
                        stringify!($value),
                        $crate::lg::__quiet(format!("{:?}", &head))
                    );
                }
            }
        }};
    }
    #[macro_export]
    macro_rules! rows {
        {
            $index_label:literal,
            $(@offset $offset:expr,)?
            $(@verticalbar $verticalbar:expr,)*
            $($(@$label:literal =>)? $values:expr),* $(,)?
        } => {{
            #![allow(unused_assignments)]
            let mut rows = $crate::lg::Rows::default();
            rows.line_number(line!());
            $(rows.offset($offset);)?
            $(rows.verticalbar($verticalbar);)*
            rows.index_label($index_label);
            $({
                let mut label = stringify!($values).to_string();
                if label.starts_with("&") {
                    label = label[1..].to_string();
                }
                $({
                    let label_: &'static str = $label;
                    label = label_.to_string();
                })?
                rows.row(label, $values);
            })*
            eprintln!("{}", rows.to_string_table());
        }};
    }
    #[macro_export]
    macro_rules! table {
        {
            $(@$name:literal => )? $values:expr $(,)?
        } => {{
            #![allow(unused_assignments)]
            let mut name = stringify!($values).to_string();
            if name.starts_with("&") {
                name = name[1..].to_string();
            }
            $({
                let name_: &'static str = $name;
                name = name_.to_string();
            })?
            let mut rows = $crate::lg::Rows::default();
            rows.line_number(line!());
            rows.table_name(name);
            #[allow(array_into_iter)]
            for (i, row) in $values.into_iter().enumerate() {
                rows.row(i.to_string(), row);
            }
            eprintln!("{}", rows.to_string_table());
        }};
    }
    #[doc(hidden)]
    pub fn __quiet(s: impl AsRef<str>) -> String {
        s.as_ref()
            .replace("340282366920938463463374607431768211455", "*") // u128
            .replace("170141183460469231731687303715884105727", "*") // i128
            .replace("18446744073709551615", "*") // u64
            .replace("9223372036854775807", "*") // i64
            .replace("-9223372036854775808", "*") // i64
            .replace("4294967295", "*") // u32
            .replace("2147483647", "*") // i32
            .replace("-2147483648", "*") // i32
            .replace("None", "*")
            .replace("Some", "")
            .replace("true", "#")
            .replace("false", ".")
            .replace(['"', '\''], "")
    }
    #[doc(hidden)]
    #[derive(Default)]
    pub struct Rows {
        line_number: String,
        index_label: String,
        offset: usize,
        verticalbars: Vec<usize>,
        table_name: String,
        rows: Vec<Row>,
    }
    impl Rows {
        pub fn line_number(&mut self, line_number: u32) -> &mut Self {
            self.line_number = format!("{}", line_number);
            self
        }

        pub fn index_label(&mut self, index_label: impl Into<String>) -> &mut Self {
            self.index_label = index_label.into();
            self
        }

        pub fn offset(&mut self, offset: usize) -> &mut Self {
            self.offset = offset;
            self
        }

        pub fn verticalbar(&mut self, verticalbar: impl IntoIterator<Item = usize>) -> &mut Self {
            self.verticalbars.extend(verticalbar);
            self
        }

        pub fn table_name(&mut self, table_name: impl Into<String>) -> &mut Self {
            self.table_name = table_name.into();
            self
        }

        pub fn row(
            &mut self,
            label: impl Into<String>,
            values: impl IntoIterator<Item = impl fmt::Debug>,
        ) -> &mut Self {
            self.rows.push(Row {
                label: label.into(),
                values: values
                    .into_iter()
                    .map(|value| __quiet(format!("{:?}", value)))
                    .collect(),
            });
            self
        }

        pub fn to_string_table(self) -> StringTable {
            let Self {
                line_number,
                index_label,
                offset,
                verticalbars,
                table_name,
                rows,
            } = self;
            let w = rows
                .iter()
                .map(|row| row.values.len())
                .max()
                .unwrap_or_default();
            let mut verticalbar_count = vec![0; w + 1];
            for &v in &verticalbars {
                if (offset..=offset + w).contains(&v) {
                    verticalbar_count[v - offset] += 1;
                }
            }
            StringTable {
                head: StringRow {
                    label: format!(
                        "{line_number}❯ {table_name}{index_label}",
                        index_label = if index_label.is_empty() {
                            String::new()
                        } else {
                            format!("[{}]", index_label)
                        }
                    ),
                    values: (offset..offset + w)
                        .map(|index| index.to_string())
                        .collect(),
                },
                body: rows
                    .iter()
                    .map(|row| StringRow {
                        label: row.label.clone(),
                        values: row.values.clone(),
                    })
                    .collect(),
                verticalbar_count,
            }
        }
    }
    struct Row {
        label: String,
        values: Vec<String>,
    }
    #[doc(hidden)]
    pub struct StringTable {
        head: StringRow,
        body: Vec<StringRow>,
        verticalbar_count: Vec<usize>,
    }
    impl fmt::Display for StringTable {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            let Self {
                head,
                body,
                verticalbar_count,
            } = self;
            let w = body
                .iter()
                .map(|row| row.values.len())
                .max()
                .unwrap_or_default();
            let label_width = once(head.label.chars().count())
                .chain(body.iter().map(|row| row.label.chars().count()))
                .max()
                .unwrap();
            let value_width = (0..w)
                .map(|j| {
                    once(j.to_string().len())
                        .chain(
                            body.iter()
                                .map(|row| row.values.get(j).map_or(0, |s| s.chars().count())),
                        )
                        .max()
                        .unwrap()
                })
                .collect::<Vec<_>>();
            // Heading
            gray(f)?;
            write!(
                f,
                "{}",
                head.to_string(label_width, &value_width, verticalbar_count, true)
            )?;
            resetln(f)?;
            // Body
            for row in body {
                write!(
                    f,
                    "{}",
                    row.to_string(label_width, &value_width, verticalbar_count, false)
                )?;
                writeln!(f)?;
            }
            Ok(())
        }
    }
    struct StringRow {
        label: String,
        values: Vec<String>,
    }
    impl StringRow {
        fn to_string(
            &self,
            label_width: usize,
            value_width: &[usize],
            varticalbars_count: &[usize],
            label_align_left: bool,
        ) -> String {
            let Self { label, values } = self;
            let w = value_width.len();
            let mut s = String::new();
            s.push_str(&if label_align_left {
                format!("{label:<label_width$} |")
            } else {
                format!("{label:^label_width$} |")
            });
            for j in 0..w {
                let value_width = value_width[j];
                s.push_str("|".repeat(varticalbars_count[j]).as_str());
                if varticalbars_count[j] == 0 && j != 0 && value_width <= 1 {
                    s.push(' ');
                }
                match values.get(j) {
                    Some(value) => {
                        s.push_str(&format!(" {value:>value_width$}",));
                    }
                    None => {
                        s.push_str(" ".repeat(value_width + 1).as_str());
                    }
                }
            }
            s
        }
    }
    const GRAY: &str = "\x1b[48;2;127;127;127;37m";
    const RESET: &str = "\x1b[0m";
    fn gray(f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{GRAY}")
    }
    fn resetln(f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(f, "{RESET}")
    }
    pub fn bools<B, I>(iter: I) -> String
    where
        B: Borrow<bool>,
        I: IntoIterator<Item = B>,
    {
        format!(
            "[{}]",
            iter.into_iter()
                .map(|b| ['.', '#'][usize::from(*(b.borrow()))])
                .collect::<String>(),
        )
    }
}
// }}}