//规定：还没有计算出的状态不能走
#include<cstdio>
#include<iostream>
#include<cstring>
#include<ctime>
#include<algorithm>
using namespace std;

const int maxn=150;
const int INF=2000000000;
const int dx[]={0,1,-1,0};
const int dy[]={1,0,0,-1};

char buf[40],c[maxn][maxn];
int n,m,d,f[maxn][maxn][maxn];

template<class T> inline bool getd(T& x)
{
	int ch=getchar();
	bool neg=false;
	while(ch!=EOF && ch!='-' && !isdigit(ch)) ch=getchar();
	if(ch==EOF) return false;
	if(ch=='-'){
		neg=true;
		ch=getchar();
	}
	x=ch-'0';
	while(isdigit(ch=getchar())) x=x*10+ch-'0';
	if(neg) x=-x;
	return true;
}

template<class M> inline void putd(M x)
{
	int p=0;
	if(x<0){
		putchar('-');
		x=-x;
	}
	if(x==0) buf[p++]=0;
	while(x){
		buf[p++]=x%10;
		x/=10;
	}
	for(int i=p-1;i>=0;i--) putchar(buf[i]+'0');
}

int dfs(int x,int y,int d)
{
//	printf("x=%d,y=%d,d=%d\n",x,y,d);
	if(x<0 || y<0 || x>m-1 || y>n-1 || c[x][y]=='L') return INF;
	if(f[x][y][d]!=-1) return f[x][y][d];
	int ans;
	ans=f[x][y][d]=INF;
	//步行
	for(int i=0;i<4;i++)
		if(f[x+dx[i]][y+dy[i]][d]!=INF)
			ans=min(ans,dfs(x+dx[i],y+dy[i],d)+1);
	//飞行
	for(int i=1;i<=d;i++){
		if(f[x+i][y][d-i]!=INF) ans=min(ans,dfs(x+i,y,d-i)+1);
		if(f[x][y+i][d-i]!=INF) ans=min(ans,dfs(x,y+i,d-i)+1);
		if(f[x-i][y][d-i]!=INF) ans=min(ans,dfs(x-i,y,d-i)+1);
		if(f[x][y-i][d-i]!=INF) ans=min(ans,dfs(x,y-i,d-i)+1);
	}
	return f[x][y][d]=ans;
}

void init()
{
	getd(m);getd(n);getd(d);
//	printf("m=%d,n=%d,d=%d\n",m,n,d);
	for(int i=0;i<m;i++)
	    for(int j=0;j<n;j++){
			int ch=getchar();
			while(ch!='P' && ch!='L') ch=getchar();
			c[i][j]=ch;
	    }
}

void work()
{
	memset(f,-1,sizeof(f));
	for(int i=0;i<=d;i++) f[m-1][n-1][i]=0;
	int x=dfs(0,0,d);
	if(x!=INF) printf("%d\n",x);
	else printf("impossible\n");
}

int main()
{
	freopen("escapea.in","r",stdin);
	freopen("escapea.out","w",stdout);
	init();
	work();
	fclose(stdin);
	fclose(stdout);
	return 0;
}