#include <stdio.h>
#include <stdlib.h>
#include <time.h>
  
long get_count(long val) {
    long count=0, i = 5;
  
    while( i <= val ) {
        count += val/i;
        i *= 5;
    }
    return count;
}
  
long get_N(long P) {
    long min = 4*P, max = 5*P, mid, zeros;
    while ( min <= max) {
        mid = (min + max)/2;
        zeros = get_count(mid);
        printf("min=%ld   max=%ld   zeros=%ld\n", min, max, zeros );
        if(zeros==P)
            return (mid - mid%5);
        if(zeros>P) {
            max = mid-1;
        } else {
            min = mid+1;
        }
        if(min>max)
            return -1;
    }
    return -1;
}
  
int main(int argc, char *argv[]) {
      
    long P, N;
      
    clock_t start = clock();
      
    FILE *f1 = fopen("fact.in", "r");
    fscanf(f1, "%ld", &P);
    fclose(f1);
  
    f1 = fopen("fact.out", "w");
      
    N = get_N(P);
    printf("get_count=%ld\nget_N=%ld\n", get_count(P), N);
      
    fprintf(f1, "%ld\n", P>0?N:1);
    fclose(f1);
      
    printf ( "%f ms\n\n", ( (double)clock() - start ) * 1000 / CLOCKS_PER_SEC);
      
    return 0;
}