#include <cstdio>
#include <string.h>

using namespace std;

bool ciur[2000000];

int main()
{
    FILE *f=fopen("ciur.in","r");
    int n,j,i,nrprime=0;
    fscanf(f,"%d",&n);
    memset(ciur,1,n+1);
    for(int i=2;i<=n;++i)
    {
        if(ciur[i])
        {
        ++nrprime;
        for(int j=i;j<=n;j+=i)
            ciur[j]=0;
        }
    }
    fclose(f);
    f=fopen("ciur.out","w");
    fprintf(f,"%d",nrprime);

    return 0;
}