#include <stdio.h>

char ciur[2000001];

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