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

FILE *fin , *fout;

int nr0(int x) {
    int nr=0,p=5;
    while(p<=x) {
        nr+=x/p;
        p*=5;
    }
    return nr;
}

int main() {
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");

    int p,st,dr,mij;
    fscanf(fin,"%d",&p);
    st=1;
    dr=1000000000;
    while(dr>st) {
        mij=(st+dr)/2;
        if(nr0(mij)<p) {
            st=mij+1;
        }
        else {
            dr=mij;
        }
    }
    fprintf(fout,"%d\n",st);

    fclose(fin);
    fclose(fout);
    return 0;
}