#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define fread(p) freopen(p,"r",stdin);
#define fwrite(p) freopen(p,"w",stdout);
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pb push_back
#define mem(s,k) memset(s, k, sizeof(s))
////--- Graph Moves---////
//const ll xx[] = {0,0,1,-1};
//const ll yy[] = {1,-1,0,0};
//const ll xx_king[] = {0,0,1,-1,1,1,-1,-1};
//const ll yy_king[] = {1,-1,0,0,1,-1,1,-1};
//const ll xx_knight[]= {-2,-1,1,2,2,1,-1,-2};
//const ll yy_knight[]= {1,2,2,1,-1,-2,-2,-1};
////------------------////
int main()
{
// fwrite("a.txt");
double t,s,q, cnt=0;
cin >> t >> s >> q;
double r=t-s, d, i,j, x=(q-1)/q;
while(r>0)
{
// cout << "he " << r << endl;
cnt++;
for(i=0, j=s; i<j && r>0; )
{
if(i==j) break;
// printf("%.12f %.12f %.6f\n",i,j,r);
i++;
j += x;
r = t-j;
}
s = j;
}
// while(s<t)
// cnt++, s*=q;
cout << cnt << endl;
}
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