#include <stdio.h>

char prim[2000005];

int main(){

FILE *file1, *file2;
int i, j, N, count=1;

file1 = fopen("ciur.in", "r");
file2 = fopen("ciur.out", "w");

fscanf(file1, "%d", &N);

memset(prim, 1, 2000005);

for(i = 3; i <= N; i+=2){
    if(prim[i]){
        ++count;
        for(j = i+i+i; j <= N; j += i<<1){
            prim[j] = 0;
        }
    }
}

fprintf(file2, "%d", count);

return 0;
}