#include<stdio.h>
char ciur[2000000];
int main(){
    int prim,n,nr=0,m,i;
    FILE *fin=fopen("ciur.in","r"),*fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    prim=2;
    while(prim*prim<=n){
        for(m=2;m<=n/prim;m++)
        ciur[prim*m]=1;
        prim++;
    }
    while(ciur[prim]==1) prim++;
for(i=2;i<=n;i++){
    if(ciur[i]==0) nr++;
}
fprintf(fout,"%d",nr);
return 0;
}