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

int main()
{
    int n=1,z, p=25;
    FILE *fin,*fout;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%d",&z);
    fclose(fin);
    //if(p==0){fprintf(fout,"1");}
    n=z*5;
    while(p<n){
        n=n-(n-p/5)/p*5;
        p=p*5;
    }
    fprintf(fout,"%d",n);
    return 0;
}