#include <stdio.h>

int N,cnt;
char prim[2000005];

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