#include<bits/stdc++.h>
#define int __int128
using namespace std;
namespace fast_IO {
#define IOSIZE 100000
	char ibuf[IOSIZE], obuf[IOSIZE], *p1 = ibuf, *p2 = ibuf, *p3 = obuf;
#define getchar() ((p1==p2)and(p2=(p1=ibuf)+fread(ibuf,1,IOSIZE,stdin),p1==p2)?(EOF):(*p1++))
#define putchar(x) ((p3==obuf+IOSIZE)&&(fwrite(obuf,p3-obuf,1,stdout),p3=obuf),*p3++=x)
#define isdigit(ch) (ch>47&&ch<58)
#define isspace(ch) (ch<33)
	template<typename T> inline T read() { T s = 0; int w = 1; char ch; while (ch = getchar(), !isdigit(ch) and (ch != EOF)) if (ch == '-') w = -1; if (ch == EOF) return false; while (isdigit(ch)) s = s * 10 + ch - 48, ch = getchar(); return s * w; }
	template<typename T> inline bool read(T &s) { s = 0; int w = 1; char ch; while (ch = getchar(), !isdigit(ch) and (ch != EOF)) if (ch == '-') w = -1; if (ch == EOF) return false; while (isdigit(ch)) s = s * 10 + ch - 48, ch = getchar(); return s *= w, true; }
	template<typename T> inline void print(T x) { if (x < 0) putchar('-'), x = -x; if (x > 9) print(x / 10); putchar(x % 10 + 48); }
	inline bool read(char &s) { while (s = getchar(), isspace(s)); return true; }
	inline bool read(char *s) { char ch; while (ch = getchar(), isspace(ch)); if (ch == EOF) return false; while (!isspace(ch)) *s++ = ch, ch = getchar(); *s = '\000'; return true; }
	inline void print(char x) { putchar(x); }
	inline void print(char *x) { while (*x) putchar(*x++); }
	inline void print(const char *x) { for (int i = 0; x[i]; i++) putchar(x[i]); }
	inline bool read(std::string& s) { s = ""; char ch; while (ch = getchar(), isspace(ch)); if (ch == EOF) return false; while (!isspace(ch)) s += ch, ch = getchar(); return true; }
	inline void print(std::string x) { for (int i = 0, n = x.size(); i < n; i++) putchar(x[i]); }
	inline bool read(bool &b) { char ch; while(ch=getchar(), isspace(ch)); b=ch^48; return true; }
	inline void print(bool b) { putchar(b+48); }
	template<typename T, typename... T1> inline int read(T& a, T1&... other) { return read(a) + read(other...); }
	template<typename T, typename... T1> inline void print(T a, T1... other) { print(a), print(other...); }
	struct Fast_IO { ~Fast_IO() { fwrite(obuf, p3 - obuf, 1, stdout); } } io;
	template<typename T> Fast_IO& operator >> (Fast_IO &io, T &b) { return read(b), io; }
	template<typename T> Fast_IO& operator << (Fast_IO &io, T b) { return print(b), io; }
#define cout io
#define cin io
#define endl '\n'
} using namespace fast_IO;
const int N=3e5+10;
int n,m,e[N];
int sumt[N],sumf[N];
int s,f[N];
int h=1,t,q[N];
inline int Y(int x) {
	return (f[x]);
}
inline int X(int x) {
	return (sumf[x]);
}
inline int K(int x) {
	return (s+sumt[x]);
}
inline bool check(int x,int val) {
	return (Y(q[x+1])-Y(q[x]))>(X(q[x+1])-X(q[x]))*val;
}
inline int Binary_Search(int L,int R,int val) {
	int ans=t;
	while (L<=R) {
		int mid=(L+R)>>1;
		if (check(mid,val)) R=mid-1,ans=mid;
		else L=mid+1;
	}
	return q[ans];
}
signed main() {
	cin>>n>>s;
	for (int i=1;i<=n;i++) {
		cin>>sumt[i]>>sumf[i];
		sumt[i]+=sumt[i-1];
		sumf[i]+=sumf[i-1];
	}
	q[++t]=0;	
	for (int i=1;i<=n;i++) {
//		for (int j=0;j<i;j++) {
//			f[i]=min(f[i],f[j]+sumt[i]*(sumf[i]-sumf[j])+s*(sumf[n]-sumf[j]));
//		}
		int j=Binary_Search(h,t,K(i));
		f[i]=f[j]+sumt[i]*(sumf[i]-sumf[j])+s*(sumf[n]-sumf[j]);
		while (h<t and (__int128)(Y(i)-Y(t))*(X(t)-X(t-1))<=(__int128)(Y(t)-Y(t-1))*(X(i)-X(t))) t--;
		q[++t]=i;
	}
	cout<<f[n]<<endl;
	return (0-0);
}