#include <stdio.h>
unsigned long n,nr,i;
int main()
{
    FILE *f1,*f2;
    f1=fopen("ciur.in","r");
    f2=fopen("ciur.out","w");
    fscanf(f1,"%lu",&n);
    bool mat[n+5];
    for(i=0;i<=n;i++)mat[i]=1;
    for(i=2;i<=n;i++)
        if(mat[i]==1)
        {
            for(long j=i+i;j<=n;j+=i)
            mat[j]=0;
            nr++;
        }
    fprintf(f2,"%lu",nr);
    return 0;
}