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

long ciur[2000000];
long n,counter;
int main() {

    FILE *fin,*fout;
    long i,j,p;
    char c;

    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");

    fscanf(fin,"%ld",&n);
    for(i=2;i<=n;i++)
        ciur[i]=i;

    counter=0;
    for(i=2;i<=n;i++) {
        if(ciur[i]) {
            counter++;

        for(j=i+i;j<=n;j+=i) {
            ciur[j]=0;
        }

    }
    }
    fprintf(fout,"%ld",counter);
    fclose(fout);
    return 0;
}