#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);

	string s;
	cin >> s;
	string t;
	while (SZ(t) < SZ(s)) t += "PER";
	int cnt = 0;
	FOR(i, 0, SZ(s))
	{
		cnt += s[i] != t[i];
	}
	cout << cnt << '\n';
	return 0;
}