#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>
#include<inttypes.h>
#include<string.h>
#include<math.h>

typedef int32_t i32;
typedef int64_t i64;

#define MAX(a,b) ((a) > (b) ? (a) : (b))
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define ABS(a) ((a) > (0) ? (a) : -(a))

void run (void) {
  i32 n;
  scanf ("%" SCNi32, &n);
  printf ("%" PRIi32 "\n", n * (n + 1) / 2);
}

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