#include <iostream>

using namespace std;

const int DIM = 2000001;

bool c[DIM];
int n, nr;
int main()
{   FILE *f=fopen("ciurul.in","r");
    FILE *g=fopen("ciurul.out", "w");

    int i,j;
    fscanf(f,"%d", &n);

    for(i=2; i<=n; ++i);
       if(!c[i])
            for (j=2 * 1;j<=n; j +=i)
               c[j] = 1;

     for(i = 2; i<=n; ++i)
                if(!c[i])
                   ++nr;
     fprintf(g , "%d" , nr);
    return 0;
}