#include <cstdio>

using namespace std;

int main()
{
    FILE * f=fopen("ciur.in","r");
    FILE * g=fopen("ciur.out","w");
    int n,nr=0;
    bool viz[2000000];
    viz[1] = 1;
    fscanf(f,"%d",&n);
    for(int i=2;i<=n;i++)
    {
        if(viz[i] == 0)
        {
            for(int j = i*i;j<=n;j=j+i)
                viz[j] = 1;
        }
    }
    for(int i=2;i<=n;i++)
    {
        if(viz[i] == 0)
            nr++;
    }
    fprintf(g,"%i",nr);
    return 0;
}