/* dp[i]=min(dp[i], dp[j]+st[i](sf[i]-sf[j])+s(sf[n]-sf[j]));

dp[i]=dp[j]+st[i](sf[i]-sf[j])+s(sf[n]-sf[j]));

dp[i]-st[i]sf[i]-ssf[n]= dp[j]-s*sf[j]- st[i]sf[j] dp[j]-ssf[j] =st[i]sf[j] + dp[i]-st[i]sf[i]-ssf[n] yj=dp[j]-ssf[j] xj=sf[j] k=st[i] b=dp[i]-st[i]sf[i]-ssf[n]

*/

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=310000;
LL dp[N], f[N], t[N], st[N], sf[N], s; int q[N];
double X(int j){ return 1.0*sf[j];}
double Y(int j){ return 1.0*(dp[j]-s*sf[j]);}
double K(int j1, int j2){return (X(j2)==X(j1))?1e18*( Y(j2)-Y(j1) ) : ( Y(j2)-Y(j1) ) / ( X(j2)-X(j1) )  ;}
int main()
{
	//freopen("a.in", "r", stdin); freopen("a.out", "w", stdout); 
    int n; scanf("%d%lld", &n, &s);
    st[0]=0; sf[0]=0; 
    for(int i=1;i<=n;i++)
    {
        scanf("%lld%lld", &t[i], &f[i]);
        st[i]=st[i-1]+t[i];
        sf[i]=sf[i-1]+f[i];
    }
    int l=1, r=1; q[1]=0; dp[0]=0;
    for(int i=1;i<=n;i++)
    {
        while(l<r && K(q[l], q[l+1]) <= st[i] ) l++;
        dp[i]=dp[q[l]] + st[i]*(sf[i]-sf[q[l]]) + s*(sf[n]-sf[q[l]]);
        while( l<r && K(q[r-1], q[r] ) >= K(q[r], i) ) r--;
        q[++r]=i;    
    }
    printf("%lld\n", dp[n]);
    return 0;
}

/*
dp[i]=min(dp[i],dp[j]+st[i]*(sf[i]-sf[j])+s*(sf[n]-sf[j]));
 
dp[i]=dp[j]+st[i]*(sf[i]-sf[j])+s*(sf[n]-sf[j]));
 
dp[i]-st[i]*sf[i]-s*sf[n]=  dp[j]-s*sf[j]- st[i]*sf[j]
dp[j]-s*sf[j] =st[i]*sf[j] + dp[i]-st[i]*sf[i]-s*sf[n]
yj=dp[j]-s*sf[j]
xj=sf[j]
k=st[i]
b=dp[i]-st[i]*sf[i]-s*sf[n]
 
*/
#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=310000;
LL dp[N],f[N],t[N],st[N],sf[N],s;int q[N];
double X(int j){ return 1.0*sf[j];}
double Y(int j){ return 1.0*(dp[j]-s*sf[j]);}
double K(int j1,int j2){return (X(j2)==X(j1))?1e18*( Y(j2)-Y(j1) ) :( Y(j2)-Y(j1) ) / ( X(j2)-X(j1) )  ;}
int main()
{
	//freopen("a.in","r",stdin);freopen("a.out","w",stdout); 
    int n;scanf("%d%lld",&n,&s);
    st[0]=0;sf[0]=0; 
    for(int i=1;i<=n;i++)
    {
        scanf("%lld%lld",&t[i],&f[i]);
        st[i]=st[i-1]+t[i];
        sf[i]=sf[i-1]+f[i];
    }
    int l=1,r=1;q[1]=0;dp[0]=0;
    for(int i=1;i<=n;i++)
    {
        while(l<r && K(q[l],q[l+1])<=st[i] ) l++;
        dp[i]=dp[q[l]]+st[i]*(sf[i]-sf[q[l]])+s*(sf[n]-sf[q[l]]);
        while( l<r && K(q[r-1],q[r] ) >= K(q[r],i) ) r--;
        q[++r]=i;    
    }
    printf("%lld\n",dp[n]);
    return 0;
}