#include<stdio.h>

void run(void){
  int v1,v2;
  scanf("%d.%d",&v1,&v2);
  int t;
  scanf("%d",&t);
  int ans=v1*t+v2*t/10000;
  printf("%d\n",ans);
  return;
}

int main(void){
  run();
  return 0;
}