#include<bits/stdc++.h>
using namespace std;

#define IN "ploaie.in"
#define OUT "ploaie.out"

#define MAX_N 2000001

bool sieve[MAX_N];

int main() {
  FILE *fin, *fout;
  fin = fopen(IN, "r");
  fout = fopen(OUT, "w");

  for (int i = 2; i * i < MAX_N; ++i)
    if (!sieve[i])
      for (int j = i * i; j < MAX_N; j += i)
        sieve[j] = true;

  int n;
  fscanf(fin, "%d", &n);

  int lastPrime = 2, sum, sqSum;
  for (int i = 3; i < MAX_N && n > 0; ++i)
    if (!sieve[i]) {
      sum = lastPrime + i;
      sqSum = sqrt(sum);

      if (sqSum * sqSum == sum) --n;

      lastPrime = i;
    }

  fprintf(fout, "%d\n", sum);

  fclose(fin);
  fclose(fout);
  return 0;
}