#include<cstdio>
int a[10005];
int main(){
  int n;
  scanf("%d",&n);
  for(int i=1,t=1;i<=10005;t++){
    int f=t;
    while(f>0){
      a[i++]=t+a[i-2];  
      f--;  
    }
  }
  printf("%d",a[n]);
  return 0;
}