#include <bits/stdc++.h>
#define l long long
#define mx 2000000
using namespace std;
ifstream din("date.in");
ofstream dout("date.out");
int n;
int i,j,k;
bitset<mx> prim;
vector<int>p;
void ceva()
{
for (l i=2;i<=mx;i++)
    if (prim[1]==0)
{
    for(l j=i*i;j<=mx;j=j+i)
        prim[j]=1;
        p.push_back(1);
}
}
int main()
{
  din >>n;
  ceva();
  for(i=0;p[i];i++)
    k++;
  dout << k;


    return 0;
}