#include<bits/stdc++.h>

using namespace std;

const int N = 1e6 + ;

typedef long long ll;

typedef long double ld;

typedef unsigned long long ull;

int n , S , l , r;

ll sumc[N] , sumt[N] , f[N];

int q[N] , c[N] , t[N];

template <typename T> inline void chkmax(T &x,T y) { x = max(x,y); }

template <typename T> inline void chkmin(T &x,T y) { x = min(x,y); }

template <typename T> inline void read(T &x)

{

    T f = ; x = ;

    char c = getchar();

    for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;

    for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';

    x *= f;

}

inline int _binary_search(int L , int R , int val)

{

        int l = L , r = R , ret = L;

        while (l <= r)

        {

                int mid = (l + r) >> ;

                if (f[q[mid + ]] - f[q[mid]] <= val * (sumc[q[mid + ]] - sumc[q[mid]]))

                {

                        ret = mid + ;

                        l = mid + ;

                }    else r = mid - ;

        }

        return ret;

}

int main()

{

        read(n); read(S);

        for (int i = ; i <= n; i++)

        {

                read(t[i]);

                read(c[i]);

                sumt[i] = sumt[i - ] + t[i];

                sumc[i] = sumc[i - ] + c[i];

        }

        f[q[l = r = ] = ] = ;

        for (int i = ; i <= n; i++)

        {

                int pos = _binary_search(l , r -  , S + sumt[i]);

                f[i] = f[q[pos]] - sumc[q[pos]] * (S + sumt[i]) + sumt[i] * sumc[i] + S * sumc[n];

                while (l < r && (f[i] - f[q[r]]) * (sumc[q[r]] - sumc[q[r - ]]) <= (f[q[r]] - f[q[r - ]]) * (sumc[i] - sumc[q[r]])) --r;

                q[++r] = i;

        }

        printf("%lld\n" , f[n]);

        return ;

}