#include <cstdio>
using namespace std;

int nr,i,j,n;
char v[2000002];

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