#include <fstream>

using namespace std;

ifstream cin("Branza.in");
ofstream cout("Branza.out");

const int N=100001;
int v[N],dq[N];

int main()
{
    int n,s,t,i,st,dr;
    long long total=0;
    t++;
    st=0;
    dr=-1;
    for(i=0;i<n;i++){
        int p;
        cin>>v[i]>>p;
        if(st<=dr && dq[st]==i-t){
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]]+s*(i-dq[dr])){
            dr--;
    }
    dq[++dr]=i;
    total+=p*(v[dq[st]+s*(i-dq[st])]);
    }
    return 0;
}