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

int cif(long i)
{
    long j;
    int c;
    c=0;
    j=i;
    while(j!=0)
    {
        j=j/10;
        c++;
    }
    return c;
}

long factorial(int i)
{
    long s;
    int l;
    s=1;
    for(l=1;l<=i;l++)
        s=s*l;
    return s;
}

int main()
{
    FILE *p,*q;
    p=fopen("fact.in","r");
    q=fopen("fact.out","w");
    long i;
    int n;
    fscanf(p,"%d",&n);
    i=0;
    while (cif(factorial(i))!=n)
    {
        i++;
    }
    fprintf(q,"%ld",i);
    printf("\ni=%ld",i);
    fclose(p);
    fclose(q);
    return 0;
}