#include <stdio.h>
#include <stdlib.h>

char c[2000001];

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