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#include<cstdio>
#include<vector>

using namespace std;

constexpr auto N = 500005;

long long DP[N];
long long A[N];
long long W[N];
long long MAX[N];

struct para {
    long long dp;
    long long w;

    para(long long dp1, long long w1) : dp(dp1), w(w1) {}
};

para max1 = para(-1, -1);
para max2 = para(-1, -1);

static void dodajMax(long long dp, long long w) {
    MAX[w] = dp;

    if (dp > max1.dp) {
        max2 = max1;
        max1 = para(dp, w);
    }
    else if (dp > max2.dp) {
        max2 = para(dp, w);
    }
}

long long max(long long a, long long b) {
    return a > b ? a : b;
}

long long maxInny(long long w) {
    if (max1.w != -1 && max1.w != w) {
        return max1.dp;
    }
    if (max2.w != -1 && max2.w != w) {
        return max2.dp;
    }
    return 0;
}

int main() {
    long long n, c;
    scanf("%lld %lld", &n, &c);

    vector<para> maksima;

    for (int i = 0; i < n; i++) {
        scanf("%lld %lld", &A[i], &W[i]);
    }

    // Najlepszy wynik do i z użyciem i;
    DP[0] = A[0];
    maksima.push_back(para(DP[0], W[0]));

    for (int i = 1; i < n; i++) {
        if (A[i] != A[i - 1]) {
            // skonsumuj maksima
            for (auto it = maksima.begin(); it != maksima.end(); it++) {
                dodajMax(it->dp, it->w);
            }
            maksima.clear();
        }

        DP[i] = A[i];
        long long r1 = MAX[W[i]] + A[i];
        long long r2 = maxInny(W[i]) + A[i] - c;
        DP[i] = max(DP[i], r1);
        DP[i] = max(DP[i], r2);
        maksima.push_back(para(DP[i], W[i]));
    }

    long long result = DP[0];
    for (int i = 0; i < n; i++) {
        result = max(result, DP[i]);
    }

    printf("%lld", result);

    return 0;
}