#include <stdio.h>
#include <stdlib.h>
#define MAXN 2000000

char ciur[1+MAXN];
int main(){
    int n, i, j;
    FILE*fi,*fo;
    fi=fopen("ciur.in","r");
    fo=fopen("ciur.out","w");
    fscanf(fi,"%d", &n);
    ciur[0]=ciur[1]=1;
    for(i=2;i*i<=n;i++)
        if(ciur[i]==0)
            for(j=i*i;j<=n;j+=i)
                ciur[j]=1;
    int ind=0;
    for(i=0;i<=n;i++)
        if(ciur[i]==0)
            ind++;
    fprintf(fo,"%d", ind);
    fclose(fi);
    fclose(fo);
    return 0;
}