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

char c[2000001];

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