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

int main()
{
    unsigned int N,P,cn1,delta=0;
    FILE *fin,*fout;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%u",&P);
    N=P*5;
    cn1=N;
    while(cn1>=5){
        cn1=cn1/5;
        delta=delta*5+1;
    }
    N=N-delta;
    fprintf(fout,"%u",N);
    return 0;
}