#include <iostream>
#include <cstring>
#include <cmath>
#define min(x,y) ((x<y) ? (x) : (y))
using namespace std;
int x,y;
float dp[1001][1001];
bool d[1001][1001];
float solve(int x,int y) {
if (dp[x][y]!= -1.0)
return dp[x][y];
if (x == 0 && y == 0)
return (dp[x][y] = 0.0);
if (x == 0 )
return (dp[x][y] = y*100);
if (y == 0)
return (dp[x][y] = x*100);
float ret;
float r1,r2,r3;
r1 = 100.0 + solve(x-1,y);
r2 = 100.0 + solve(x,y-1);
ret = min(r1,r2);
if (d[x][y]) {
r3 = solve(x-1,y-1);
r3 = r3 + 141.42;
ret = min(ret,r3);
}
dp[x][y] = ret;
return ret;
}
int main() {
cin >> x >> y;
int k;
int d1,d2;
cin >> k;
memset(dp,-1.0,sizeof dp);
memset(d,false,sizeof d);
for (int i=0;i<k;i++) {
cin >> d1 >> d2;
d[d1][d2]=true;
}
float dist = solve(x,y);
int ans = dist;
if (dist - ans > 0.5) {
ans++;
}
cout << ans << endl;
}
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