#include <cstdio>

#define file_in "branza.in"
#define file_out "branza.out"

int n,s,t;
long long c[101000];
long long m[101000];

void citire()
{
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	scanf("%d %d %d", &n, &s, &t);
	for (int i=0;i<n;++i)
		 scanf("%lld %lld", &c[i], &m[i]);
}

void solve()
{
	int i,p,u;
	long long d[101000];
	
	p=1;
	u=0;
	long long sol=0; 
	
	for (i=0;i<n;++i)
	{
		while(p<=u && c[i]<=c[d[u]]+s*(i-d[u])) u--;
		d[++u]=i;
		sol+=(long long)(c[d[p]]+s*(i-d[p]))*m[i];
		if (d[p]<i-t) p++;
	}
	
	printf("%lld", sol);
}

int main()
{
	citire();
	solve();
	
	fclose(stdin);
	fclose(stdout);
	
	return 0;
	
}