#include <fstream>
std::ifstream f("branza.in");std::ofstream g("branza.out");long long n,s,t,v[1<<17],d[1<<17],p=1,q,c,r,i;int main(){f>>n>>s>>t;while(n-i++){f>>v[i]>>c;while(s*(i-d[q])+v[d[q]]>v[i]&&p<=q)--q;d[++q]=i;if(i-d[p]>t)++p;r+=c*(s*(i-d[p])+v[d[p]]);}g<<r;}