#include #include using std::endl; int main() { long long n,r,avg; std::cin>>n>>r>>avg; std::multimap chengji; long long ai,bi; double pre_avg=0; for(long long i=0;i<n;i++) { std::cin>>ai>>bi; chengji.insert(std::pair(bi,ai)); pre_avg+=ai; } long long mubiao=avg*n; // std::cout<<pre_avg<<" "<<mubiao<<endl; long long result=0; for(auto i=chengji.begin();i!=chengji.end()&&pre_avg<=mubiao;i++) { long long chengji2=i->second; long long sub=r-chengji2; if(pre_avg+sub<mubiao) { pre_avg+=sub; result=result+(sub*i->first); //std::cout<<pre_avg<<"\n"; } else while(chengji2<r&&pre_avg<mubiao) { pre_avg++; result+=i->first; } } std::cout<<result<<endl; }