#include<stdio.h>#include<string.h>#include<algorithm>#include<math.h>#include<iostream>using namespace std;long long dp[10005];int sumt[10005],sumf[10005];long long G(int x,int y){return dp[x]-dp[y];}long long S(int x,int y){return sumt[x]-sumt[y];}int q[10005],r,f;void init(){r=f=0;}int main(){int n,m;scanf("%d",&n);scanf("%d",&m);for(int i=1;i<=n;i++)scanf("%d%d",&sumt[i],&sumf[i]);for(int i=n-1;i>0;i--){sumt[i]+=sumt[i+1];sumf[i]+=sumf[i+1];}init();q[++r]=n+1;for(int i=n;i>0;i--){while(f+1<r&&G(q[f+2],q[f+1])<=sumf[i]*S(q[f+2],q[f+1]))f++;int tem=q[f+1];dp[i]=dp[tem]+(m+sumt[i]-sumt[tem])*sumf[i];q[++r]=i;for(int j=r-1;j-1>f;j--){int x=q[j-1],y=q[j],z=q[j+1];if(!(G(y,x)*S(z,y)<G(z,y)*S(y,x)))q[j]=q[r--];elsebreak;}}printf("%lldn",dp[1]);return 0;}
